Cyclic TETRAPYRROLES based on the corrin skeleton.
Cobamides are a class of compounds that function as cofactors in various enzymatic reactions, containing a corrin ring similar to vitamin B12, but with different substituents on the benzimidazole moiety, and can be found in certain bacteria and archaea.
A cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. INTRINSIC FACTOR is important for the assimilation of vitamin B 12.
A group of carrier proteins which bind with VITAMIN B12 in the BLOOD and aid in its transport. Transcobalamin I migrates electrophoretically as a beta-globulin, while transcobalamins II and III migrate as alpha-globulins.
A trace element that is a component of vitamin B12. It has the atomic symbol Co, atomic number 27, and atomic weight 58.93. It is used in nuclear weapons, alloys, and pigments. Deficiency in animals leads to anemia; its excess in humans can lead to erythrocytosis.
A chlorinated hydrocarbon used as an industrial solvent and cooling liquid in electrical transformers. It is a potential carcinogen.
A basic science concerned with the composition, structure, and properties of matter; and the reactions that occur between substances and the associated energy exchange.
Dietary practice of completely avoiding meat products in the DIET, consuming VEGETABLES, CEREALS, and NUTS. Some vegetarian diets called lacto-ovo also include milk and egg products.
A nutritional condition produced by a deficiency of VITAMIN B 12 in the diet, characterized by megaloblastic anemia. Since vitamin B 12 is not present in plants, humans have obtained their supply from animal products, from multivitamin supplements in the form of pills, and as additives to food preparations. A wide variety of neuropsychiatric abnormalities is also seen in vitamin B 12 deficiency and appears to be due to an undefined defect involving myelin synthesis. (From Cecil Textbook of Medicine, 19th ed, p848)
VITAMIN B 6 refers to several PICOLINES (especially PYRIDOXINE; PYRIDOXAL; & PYRIDOXAMINE) that are efficiently converted by the body to PYRIDOXAL PHOSPHATE which is a coenzyme for synthesis of amino acids, neurotransmitters (serotonin, norepinephrine), sphingolipids, and aminolevulinic acid. During transamination of amino acids, pyridoxal phosphate is transiently converted into PYRIDOXAMINE phosphate. Although pyridoxine and Vitamin B 6 are still frequently used as synonyms, especially by medical researchers, this practice is erroneous and sometimes misleading (EE Snell; Ann NY Acad Sci, vol 585 pg 1, 1990). Most of vitamin B6 is eventually degraded to PYRIDOXIC ACID and excreted in the urine.
Retinol and derivatives of retinol that play an essential role in metabolic functioning of the retina, the growth of and differentiation of epithelial tissue, the growth of bone, reproduction, and the immune response. Dietary vitamin A is derived from a variety of CAROTENOIDS found in plants. It is enriched in the liver, egg yolks, and the fat component of dairy products.
Organic substances that are required in small amounts for maintenance and growth, but which cannot be manufactured by the human body.
A vitamin that includes both CHOLECALCIFEROLS and ERGOCALCIFEROLS, which have the common effect of preventing or curing RICKETS in animals. It can also be viewed as a hormone since it can be formed in SKIN by action of ULTRAVIOLET RAYS upon the precursors, 7-dehydrocholesterol and ERGOSTEROL, and acts on VITAMIN D RECEPTORS to regulate CALCIUM in opposition to PARATHYROID HORMONE.

A corrinoid-dependent catabolic pathway for growth of a Methylobacterium strain with chloromethane. (1/71)

Methylobacterium sp. strain CM4, an aerobic methylotrophic alpha-proteobacterium, is able to grow with chloromethane as a carbon and energy source. Mutants of this strain that still grew with methanol, methylamine, or formate, but were unable to grow with chloromethane, were previously obtained by miniTn5 mutagenesis. The transposon insertion sites in six of these mutants mapped to two distinct DNA fragments. The sequences of these fragments, which extended over more than 17 kb, were determined. Sequence analysis, mutant properties, and measurements of enzyme activity in cell-free extracts allowed the definition of a multistep pathway for the conversion of chloromethane to formate. The methyl group of chloromethane is first transferred by the protein CmuA (cmu: chloromethane utilization) to a corrinoid protein, from where it is transferred to H4folate by CmuB. Both CmuA and CmuB display sequence similarity to methyltransferases of methanogenic archaea. In its C-terminal part, CmuA is also very similar to corrinoid-binding proteins, indicating that it is a bifunctional protein consisting of two domains that are expressed as separate polypeptides in methyl transfer systems of methanogens. The methyl group derived from chloromethane is then processed by means of pterine-linked intermediates to formate by a pathway that appears to be distinct from those already described in Methylobacterium. Remarkable features of this pathway for the catabolism of chloromethane thus include the involvement of a corrinoid-dependent methyltransferase system for dehalogenation in an aerobe and a set of enzymes specifically involved in funneling the C1 moiety derived from chloromethane into central metabolism.  (+info)

Methanol:coenzyme M methyltransferase from Methanosarcina barkeri -- substitution of the corrinoid harbouring subunit MtaC by free cob(I)alamin. (2/71)

Methyl-coenzyme M formation from coenzyme M and methanol in Methanosarcina barkeri is catalysed by an enzyme system composed of three polypeptides MtaA, MtaB and MtaC, the latter of which harbours a corrinoid prosthetic group. We report here that MtaC can be substituted by free cob(I)alamin which is methylated with methanol in an MtaB-catalysed reaction and demethylated with coenzyme M in an MtaA-catalysed reaction. Methyl transfer from methanol to coenzyme M was found to proceed at a relatively high specific activity at micromolar concentrations of cob(I)alamin. This finding was surprising because the methylation of cob(I)alamin catalysed by MtaB alone and the demethylation of methylcob(III)alamin catalysed by MtaA alone exhibit apparent Km for cob(I)alamin and methylcob(III)alamin of above 1 mm. A possible explanation is that MtaA positively affects the MtaB catalytic efficiency and vice versa by decreasing the apparent Km for their corrinoid substrates. Activation of MtaA by MtaB was methanol-dependent. In the assay for methanol:coenzyme M methyltransferase activity cob(I)alamin could be substituted by cob(I)inamide which is devoid of the nucleotide loop. Substitution was, however, only possible when the assays were supplemented with imidazole: approximately 1 mm imidazole being required for half-maximal activity. Methylation of cob(I)inamide with methanol was found to be dependent on imidazole but not on the demethylation of methylcob(III)inamide with coenzyme M. The demethylation reaction was even inhibited by imidazole. The structure and catalytic mechanism of the MtaABC complex are compared with the cobalamin-dependent methionine synthase.  (+info)

Native corrinoids from Clostridium cochlearium are adeninylcobamides: spectroscopic analysis and identification of pseudovitamin B(12) and factor A. (3/71)

The corrinoids from the obligate anaerobe Clostridium cochlearium were extracted as a mixture of Co(beta)-cyano derivatives. From 50 g of frozen cells, approximately 2 mg (1.5 micromol) of B(12) derivatives was obtained as a crystalline sample. Analysis of the corrinoid sample of C. cochlearium by a combination of high-pressure liquid chromatography and UV-Vis absorbance spectroscopy revealed the presence of three cyano corrinoids in a ratio of about 3:1:1. The spectroscopic data acquired for the sample indicated the main components to be pseudovitamin B(12) (Co(beta)-cyano-7"-adeninylcobamide) (60%) and factor A (Co(beta)-cyano-7"-[2-methyl]adeninylcobamide) (20%). Authentic pseudovitamin B(12) was prepared by guided biosynthesis from cobinamide and adenine. Both pseudovitamin B(12) and its homologue, factor A, were subjected to complete spectroscopic analysis by UV-Vis, circular dichroism, mass spectrometry, and by one- and two-dimensional (1)H, (13)C-, and (15)N nuclear magnetic resonance (NMR) spectroscopy. The third component was indicated by the mass spectra to be an isomer of factor A and is likely (according to NMR) to be 7"-[N(6)-methyl]-adeninylcobamide, a previously unknown corrinoid. C. cochlearium thus biosynthesizes as its native "complete" B(12) cofactors the 7"-adeninylcobamides and two homologous corrinoids, in which the nucleotide base is a methylated adenine.  (+info)

The enigma of cobalamin (Vitamin B12) biosynthesis in Porphyromonas gingivalis. Identification and characterization of a functional corrin pathway. (4/71)

The ability of Porphyromonas gingivalis to biosynthesize tetrapyrroles de novo has been investigated. Extracts of the bacterium do not possess activity for 5- aminolevulinic-acid dehydratase or porphobilinogen deaminase, two key enzymes involved in the synthesis of uroporphyrinogen III. Similarly, it was not possible to detect any genetic evidence for these early enzymes with the use of degenerate polymerase chain reaction. However, the bacterium does appear to harbor some of the enzymes for cobalamin biosynthesis since cobyric acid, a pathway intermediate, was converted into cobinamide. Furthermore, degenerate polymerase chain reaction with primers to cbiP, which encodes cobyric-acid synthase, produced a fragment with a high degree of identity to Salmonella typhimurium cbiP. Indeed, the recently released genome sequence data confirmed the presence of cbiP together with 14 other genes of the cobalamin pathway. A number of these genes were cloned and functionally characterized. Although P. gingivalis harbors all the genes necessary to convert precorrin-2 into cobalamin, it is missing the genes for the synthesis of precorrin-2. Either the organism has a novel pathway for the synthesis of precorrin-2, or more likely, it has lost this early part of the pathway. The remainder of the pathway may be being maintained to act as a salvage route for corrin synthesis.  (+info)

The Na(+)-translocating methyltransferase complex from methanogenic archaea. (5/71)

Methanogenic archaea are dependent on sodium ions for methane formation. A sodium ion-dependent step has been shown to be methyl transfer from N(5)-methyltetrahydromethanopterin to coenzyme M. This exergonic reaction (DeltaG degrees '=-30 kJ/mol) is catalyzed by a Na(+)-translocating membrane-associated multienzyme complex composed of eight different subunits, MtrA-H. Subunit MtrA harbors a cob(I)amide prosthetic group which is methylated and demethylated in the catalytic cycle, demethylation being sodium ion-dependent. Based on the finding that in the cob(II)amide oxidation state the corrinoid is bound in a base-off/His-on configuration it is proposed that methyl transfer from MtrA to coenzyme M is associated with a conformational change of the protein and that this change drives the electrogenic translocation of the sodium ions.  (+info)

Identification and in vivo characterization of PpaA, a regulator of photosystem formation in Rhodobacter sphaeroides. (6/71)

A regulatory protein, PpaA, involved in photosystem formation in the anoxygenic phototrophic proteobacterium Rhodobacter sphaeroides has been identified and characterized in vivo. Based on the phenotypes of cells expressing the ppaA gene in extra copy and on the phenotype of the ppaA null mutant, it was concluded that PpaA activates photopigment production and puc operon expression under aerobic conditions. This is in contrast to the function of the PpaA homologue from Rhodobacter capsulatus, AerR, which acts as a repressor under aerobic conditions [Dong, C., Elsen, S., Swem, L. R. & Bauer, C. E. (2002). J Bacteriol 184, 2805-2814]. The expression of the ppaA gene increases several-fold in response to a decrease in oxygen tension, suggesting that the PpaA protein is active under conditions of low or no oxygen. However, no discernible phenotype of a ppaA null mutant was observed under anaerobic conditions tested thus far. The photosystem gene repressor PpsR mediates repression of ppaA gene expression under aerobic conditions. Sequence analysis of PpaA homologues from several anoxygenic phototrophic bacteria revealed a putative corrinoid-binding domain. It is suggested that PpaA binds a corrinoid cofactor and the availability or structure of this cofactor affects PpaA activity.  (+info)

ABC transporter for corrinoids in Halobacterium sp. strain NRC-1. (7/71)

We report evidence for the existence of a putative ABC transporter for corrinoid utilization in the extremely halophilic archaeon Halobacterium sp. strain NRC-1. Results from genetic and nutritional analyses of Halobacterium showed that mutants with lesions in open reading frames (ORFs) Vng1370G, Vng1371Gm, and Vng1369G required a 10(5)-fold higher concentration of cobalamin for growth than the wild-type or parent strain. The data support the conclusion that these ORFs encode orthologs of the bacterial cobalamin ABC transporter permease (btuC; Vng1370G), ATPase (btuD; Vng1371Gm), and substrate-binding protein (btuF; Vng1369G) components. Mutations in the Vng1370G, Vng1371Gm, and Vng1369G genes were epistatic, consistent with the hypothesis that their products work together to accomplish the same function. Extracts of btuF mutant strains grown in the presence of cobalamin did not contain any cobalamin molecules detectable by a sensitive bioassay, whereas btuCD mutant strain extracts did. The data are consistent with the hypothesis that the BtuF protein is exported to the extracellular side of the cell membrane, where it can bind cobalamin in the absence of BtuC and BtuD. Our data also provide evidence for the regulation of corrinoid transport and biosynthesis. Halobacterium synthesized cobalamin in a chemically defined medium lacking corrinoid precursors. To the best of our knowledge, this is the first genetic analysis of an archaeal corrinoid transport system.  (+info)

Evidence for the involvement of corrinoids and factor F430 in the reductive dechlorination of 1,2-dichloroethane by Methanosarcina barkeri. (8/71)

Cobalamin and the native and diepimeric forms of factor F430 catalyzed the reductive dechlorination of 1,2-dichloroethane (1,2-DCA) to ethylene or chloroethane (CA) in a buffer with Ti(III) citrate as the electron donor. Ethylene was the major product in the cobalamin-catalyzed transformation, and the ratio of ethylene to CA formed was 25:1. Native F430 and 12,13-di-epi-F430 produced ethylene and CA in ratios of about 2:1 and 1:1, respectively. Cobalamin dechlorinated 1,2-DCA much faster than did factor F430. Dechlorination rates by all three catalysts showed a distinct pH dependence, correlated in a linear manner with the catalyst concentration and doubled with a temperature increase of 10 degrees C. Crude and boiled cell extracts of Methanosarcina barkeri also dechlorinated 1,2-DCA to ethylene and CA with Ti(III) citrate as the reductant. The catalytic components in boiled extracts were heat and oxygen stable and had low molecular masses. Fractionation of boiled extracts by a hydrophobic interaction column revealed that part of the dechlorinating components had a hydrophilic and part had a hydrophobic character. These chemical properties of the dechlorinating components and spectral analysis of boiled extracts indicated that corrinoids or factor F430 was responsible for the dechlorinations. The ratios of 3:1 to 7:1 of ethylene and CA formed by cell extracts suggested that both cofactors were concomitantly active.  (+info)

Corrinoids are a class of compounds that include vitamin B12 and its analogs. Vitamin B12 is an essential nutrient for humans and other animals, playing a critical role in the synthesis of DNA, the maintenance of the nervous system, and the metabolism of fatty acids and amino acids.

The corrinoid ring is the structural backbone of vitamin B12 and its analogs. It is a complex, planar molecule made up of four pyrrole rings joined together in a macrocycle. The corrinoid ring contains a central cobalt ion, which can form coordination bonds with various ligands, including organic groups such as methyl, hydroxo, and cyano.

Corrinoids can be found in a wide variety of foods, including meat, dairy products, fish, eggs, and some fortified plant-based foods. They are also produced by certain bacteria, which can synthesize the corrinoid ring and the cobalt ion de novo. Some corrinoids have biological activity similar to vitamin B12, while others do not.

In addition to their role in human nutrition, corrinoids are also used in industrial applications, such as the production of antibiotics and other pharmaceuticals. They are also used as catalysts in chemical reactions, due to their ability to form stable coordination complexes with various ligands.

Cobamides are a class of compounds that are structurally related to vitamin B12 (cobalamin). They consist of a corrin ring, which is a large heterocyclic ring made up of four pyrrole rings, and a cobalt ion in the center. The lower axial ligand of the cobalt ion can be a variety of different groups, including cyano, hydroxo, methyl, or 5'-deoxyadenosyl groups.

Cobamides are involved in a number of important biological processes, including the synthesis of amino acids and nucleotides, the metabolism of fatty acids and cholesterol, and the regulation of gene expression. They function as cofactors for enzymes called cobamide-dependent methyltransferases, which transfer methyl groups (CH3) from one molecule to another.

Cobamides are found in a wide variety of organisms, including bacteria, archaea, and eukaryotes. In humans, the most important cobamide is vitamin B12, which is essential for the normal functioning of the nervous system and the production of red blood cells. Vitamin B12 deficiency can lead to neurological problems and anemia.

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that plays a crucial role in the synthesis of DNA, formation of red blood cells, and maintenance of the nervous system. It is involved in the metabolism of every cell in the body, particularly affecting DNA regulation and neurological function.

Vitamin B12 is unique among vitamins because it contains a metal ion, cobalt, from which its name is derived. This vitamin can be synthesized only by certain types of bacteria and is not produced by plants or animals. The major sources of vitamin B12 in the human diet include animal-derived foods such as meat, fish, poultry, eggs, and dairy products, as well as fortified plant-based milk alternatives and breakfast cereals.

Deficiency in vitamin B12 can lead to various health issues, including megaloblastic anemia, fatigue, neurological symptoms such as numbness and tingling in the extremities, memory loss, and depression. Since vitamin B12 is not readily available from plant-based sources, vegetarians and vegans are at a higher risk of deficiency and may require supplementation or fortified foods to meet their daily requirements.

Transcobalamins are a group of proteins in the human body that are responsible for the transport of vitamin B12, also known as cobalamin. There are three main types of transcobalamins:

1. Transcobalamin I (also known as haptocorrin or R-binders): This is a protein produced in various tissues, including the salivary glands and gastric mucosa. It binds to vitamin B12 in the stomach and protects it from degradation by digestive enzymes. However, this form of vitamin B12 is not available for absorption and must be converted to other forms.

2. Transcobalamin II: This is a protein produced mainly in the kidneys and intestines. It binds to vitamin B12 that has been freed from its binding proteins in the stomach and facilitates its absorption in the intestine. Once absorbed, transcobalamin II transports vitamin B12 to tissues throughout the body.

3. Transcobalamin III (also known as intrinsic factor): This is a protein produced by the parietal cells of the stomach. It binds to vitamin B12 and protects it from degradation in the acidic environment of the stomach. Intrinsic factor is essential for the absorption of vitamin B12 in the intestine, as it facilitates its transport across the intestinal wall.

Deficiencies in transcobalamins can lead to vitamin B12 deficiency, which can result in a range of health problems, including anemia, fatigue, neurological symptoms, and developmental delays in children.

Cobalt is a chemical element with the symbol Co and atomic number 27. It is a hard, silver-white, lustrous, and brittle metal that is found naturally only in chemically combined form, except for small amounts found in meteorites. Cobalt is used primarily in the production of magnetic, wear-resistant, and high-strength alloys, as well as in the manufacture of batteries, magnets, and pigments.

In a medical context, cobalt is sometimes used in the form of cobalt-60, a radioactive isotope, for cancer treatment through radiation therapy. Cobalt-60 emits gamma rays that can be directed at tumors to destroy cancer cells. Additionally, small amounts of cobalt are present in some vitamin B12 supplements and fortified foods, as cobalt is an essential component of vitamin B12. However, exposure to high levels of cobalt can be harmful and may cause health effects such as allergic reactions, lung damage, heart problems, and neurological issues.

Tetrachloroethylene, also known as perchloroethylene or "perc," is an organic compound with the formula C2Cl4. It is a colorless, volatile liquid with a sweet and somewhat unpleasant smell and taste. It is widely used for dry cleaning of clothing and textiles, and as a solvent in various industrial applications.

In a medical context, tetrachloroethylene is primarily known as a potential occupational hazard and environmental contaminant. Exposure to high levels of this chemical can cause a range of adverse health effects, including irritation of the eyes, nose, and throat, dizziness, headaches, and respiratory problems. Long-term exposure has been linked to an increased risk of certain types of cancer, such as bladder, kidney, and non-Hodgkin lymphoma.

It is important for individuals who work with tetrachloroethylene or are exposed to it in their environment to take appropriate precautions to minimize their exposure and protect their health. This may include using proper ventilation, wearing protective equipment, and following established safety protocols.

In the context of medicine, "chemistry" often refers to the field of study concerned with the properties, composition, and structure of elements and compounds, as well as their reactions with one another. It is a fundamental science that underlies much of modern medicine, including pharmacology (the study of drugs), toxicology (the study of poisons), and biochemistry (the study of the chemical processes that occur within living organisms).

In addition to its role as a basic science, chemistry is also used in medical testing and diagnosis. For example, clinical chemistry involves the analysis of bodily fluids such as blood and urine to detect and measure various substances, such as glucose, cholesterol, and electrolytes, that can provide important information about a person's health status.

Overall, chemistry plays a critical role in understanding the mechanisms of diseases, developing new treatments, and improving diagnostic tests and techniques.

A vegetarian diet is a type of eating pattern that excludes meat, poultry, and fish, and sometimes other animal products like eggs, dairy, or honey, depending on the individual's specific dietary choices. There are several types of vegetarian diets, including:

1. Ovo-vegetarian: This diet includes vegetables, fruits, grains, nuts, seeds, dairy products, and eggs but excludes meat, poultry, and fish.
2. Lacto-vegetarian: This diet includes vegetables, fruits, grains, nuts, seeds, dairy products, and eggs but excludes meat, poultry, fish, and sometimes eggs.
3. Ovo-lacto vegetarian: This is the most common type of vegetarian diet and includes vegetables, fruits, grains, nuts, seeds, dairy products, and eggs but excludes meat, poultry, and fish.
4. Vegan: This diet excludes all animal products, including meat, poultry, fish, dairy, eggs, and sometimes honey or other bee products.
5. Fruitarian: This is a more restrictive form of veganism that includes only fruits, nuts, seeds, and other plant foods that can be harvested without killing the plant.
6. Raw vegan: This diet includes only raw fruits, vegetables, nuts, seeds, and other plant foods that have not been cooked or processed above 115°F (46°C).

Vegetarian diets can provide a range of health benefits, including lower risks of heart disease, high blood pressure, type 2 diabetes, and certain cancers. However, it is important to ensure that vegetarian diets are well-planned and nutritionally adequate to meet individual nutrient needs, particularly for nutrients like vitamin B12, iron, calcium, and omega-3 fatty acids.

Vitamin B12 deficiency is a condition characterized by insufficient levels of vitamin B12 in the body, leading to impaired production of red blood cells, nerve function damage, and potential neurological complications. Vitamin B12 is an essential nutrient that plays a crucial role in DNA synthesis, fatty acid metabolism, and maintaining the health of the nervous system.

The medical definition of vitamin B12 deficiency includes:

1. Reduced serum or whole blood vitamin B12 concentrations (typically below 200 pg/mL or 145 pmol/L)
2. Presence of clinical symptoms and signs, such as:
* Fatigue, weakness, and lethargy
* Pale skin, shortness of breath, and heart palpitations due to anemia (megaloblastic or macrocytic anemia)
* Neurological symptoms like numbness, tingling, or burning sensations in the hands and feet (peripheral neuropathy), balance problems, confusion, memory loss, and depression
3. Laboratory findings consistent with deficiency, such as:
* Increased mean corpuscular volume (MCV) of red blood cells
* Reduced numbers of red and white blood cells and platelets in severe cases
* Elevated homocysteine and methylmalonic acid levels in the blood due to impaired metabolism

The most common causes of vitamin B12 deficiency include dietary insufficiency (common in vegetarians and vegans), pernicious anemia (an autoimmune condition affecting intrinsic factor production), gastrointestinal disorders (such as celiac disease, Crohn's disease, or gastric bypass surgery), and certain medications that interfere with vitamin B12 absorption.

Untreated vitamin B12 deficiency can lead to severe complications, including irreversible nerve damage, cognitive impairment, and increased risk of cardiovascular diseases. Therefore, prompt diagnosis and treatment are essential for preventing long-term health consequences.

Medical Definition of Vitamin B6:

Vitamin B6, also known as pyridoxine, is a water-soluble vitamin that plays a crucial role in various bodily functions. It is involved in the process of making serotonin and norepinephrine, which are chemicals that transmit signals in the brain. Vitamin B6 is also necessary for the formation of myelin, a protein layer that forms around nerve cells. Additionally, it helps the body to metabolize proteins, carbohydrates, and fats, and is involved in the creation of red blood cells.

Vitamin B6 can be found in a wide variety of foods, including poultry, seafood, bananas, potatoes, and fortified cereals. A deficiency in vitamin B6 can lead to anemia, confusion, and a weakened immune system. On the other hand, excessive intake of vitamin B6 can cause nerve damage and skin lesions. It is important to maintain appropriate levels of vitamin B6 through a balanced diet and, if necessary, supplementation under the guidance of a healthcare provider.

Medical Definition of Vitamin A:

Vitamin A is a fat-soluble vitamin that is essential for normal vision, immune function, and cell growth. It is also an antioxidant that helps protect the body's cells from damage caused by free radicals. Vitamin A can be found in two main forms: preformed vitamin A, which is found in animal products such as dairy, fish, and meat, particularly liver; and provitamin A carotenoids, which are found in plant-based foods such as fruits, vegetables, and vegetable oils.

The most active form of vitamin A is retinoic acid, which plays a critical role in the development and maintenance of the heart, lungs, kidneys, and other organs. Vitamin A deficiency can lead to night blindness, dry skin, and increased susceptibility to infections. Chronic vitamin A toxicity can cause nausea, dizziness, headaches, coma, and even death.

Vitamins are organic substances that are essential in small quantities for the normal growth, development, and maintenance of life in humans. They are required for various biochemical functions in the body such as energy production, blood clotting, immune function, and making DNA.

Unlike macronutrients (carbohydrates, proteins, and fats), vitamins do not provide energy but they play a crucial role in energy metabolism. Humans require 13 essential vitamins, which can be divided into two categories: fat-soluble and water-soluble.

Fat-soluble vitamins (A, D, E, and K) are stored in the body's fat tissues and liver, and can stay in the body for a longer period of time. Water-soluble vitamins (B-complex vitamins and vitamin C) are not stored in the body and need to be replenished regularly through diet or supplementation.

Deficiency of vitamins can lead to various health problems, while excessive intake of certain fat-soluble vitamins can also be harmful due to toxicity. Therefore, it is important to maintain a balanced diet that provides all the essential vitamins in adequate amounts.

Vitamin D is a fat-soluble secosteroid that is crucial for the regulation of calcium and phosphate levels in the body, which are essential for maintaining healthy bones and teeth. It can be synthesized by the human body when skin is exposed to ultraviolet-B (UVB) rays from sunlight, or it can be obtained through dietary sources such as fatty fish, fortified dairy products, and supplements. There are two major forms of vitamin D: vitamin D2 (ergocalciferol), which is found in some plants and fungi, and vitamin D3 (cholecalciferol), which is produced in the skin or obtained from animal-derived foods. Both forms need to undergo two hydroxylations in the body to become biologically active as calcitriol (1,25-dihydroxyvitamin D3), the hormonally active form of vitamin D. This activated form exerts its effects by binding to the vitamin D receptor (VDR) found in various tissues, including the small intestine, bone, kidney, and immune cells, thereby influencing numerous physiological processes such as calcium homeostasis, bone metabolism, cell growth, and immune function.

Corrinoids at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "The Nomenclature of Corrinoids" at chem. ... Corrinoids are a group of compounds based on the skeleton of corrin, a cyclic system containing four pyrrole rings similar to ... Absorption of the corrinoid on a solid phase, allows detection of cyanide even in colored samples, rendering this method ... The binding of cyanide to the corrinoid cobalt center leads to a color change from orange to violet. Quantification of the ...
Dimethylamine---corrinoid+protein+Co-methyltransferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH ... Dimethylamine-corrinoid protein Co-methyltransferase (EC 2.1.1.249, mtbB (gene), dimethylamine methyltransferase) is an enzyme ... This enzyme catalyses the following chemical reaction dimethylamine + [Co(I) dimethylamine-specific corrinoid protein] ⇌ {\ ... Krzycki JA (October 2004). "Function of genetically encoded pyrrolysine in corrinoid-dependent methylamine methyltransferases ...
Methylamine---corrinoid+protein+Co-methyltransferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH) ... Methylamine-corrinoid protein Co-methyltransferase (EC 2.1.1.248, mtmB (gene), monomethylamine methyltransferase) is an enzyme ... Burke SA, Krzycki JA (June 1997). "Reconstitution of Monomethylamine:Coenzyme M methyl transfer with a corrinoid protein and ... This enzyme catalyses the following chemical reaction methylamine + [Co(I) methylamine-specific corrinoid protein] ⇌ {\ ...
Tetramethylammonium---corrinoid+protein+Co-methyltransferase at the U.S. National Library of Medicine Medical Subject Headings ... Tetramethylammonium-corrinoid protein Co-methyltransferase (EC 2.1.1.252, mtqB (gene), tetramethylammonium methyltransferase) ... This enzyme catalyses the following chemical reaction tetramethylammonium + [Co(I) tetramethylammonium-specific corrinoid ... protein] ⇌ {\displaystyle \rightleftharpoons } [methyl-Co(III) tetramethylammonium-specific corrinoid protein] + trimethylamine ...
Trimethylamine---corrinoid+protein+Co-methyltransferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH ... Trimethylamine-corrinoid protein Co-methyltransferase (EC 2.1.1.250, mttB (gene), trimethylamine methyltransferase) is an ... This enzyme catalyses the following chemical reaction trimethylamine + [Co(I) trimethylamine-specific corrinoid protein] ⇌ {\ ... Krzycki JA (October 2004). "Function of genetically encoded pyrrolysine in corrinoid-dependent methylamine methyltransferases ...
... tetramethylammonium-specific corrinoid protein] This enzyme catalyses the transfer of a methyl group from a corrinoid protein. ... methyl-Co(III)+tetramethylammonium-specific+corrinoid+protein):coenzyme+M+methyltransferase at the U.S. National Library of ... Methyl-Co(III) tetramethylammonium-specific corrinoid protein):coenzyme M methyltransferase (EC 2.1.1.253, methyltransferase 2 ... This enzyme catalyses the following chemical reaction [methyl-Co(III) tetramethylammonium-specific corrinoid protein] + ...
Burke SA, Krzycki JA (August 1995). "Involvement of the "A" isozyme of methyltransferase II and the 29-kilodalton corrinoid ... methyl-Co(III)+methylamine-specific+corrinoid+protein):coenzyme+M+methyltransferase at the U.S. National Library of Medicine ... This enzyme catalyses the following chemical reaction [methyl-Co(III) methylamine-specific corrinoid protein] + coenzyme M ⇌ ... Methyl-Co(III) methylamine-specific corrinoid protein):coenzyme M methyltransferase (EC 2.1.1.247, methyltransferase 2, MT2, ...
... methanol-specific corrinoid protein] Free methylcob(I)alamin can substitute for the corrinoid protein in vitro. LeClerc GM, ... methyl-Co(III)+methanol-specific+corrinoid+protein):coenzyme+M+methyltransferase at the U.S. National Library of Medicine ... Methyl-Co(III) methanol-specific corrinoid protein):coenzyme M methyltransferase (EC 2.1.1.246, methyltransferase 2, mtaA (gene ... This enzyme catalyses the following chemical reaction [methyl-Co(III) methanol-specific corrinoid protein] + coenzyme M ⇌ ...
A further type of synthesis occurs through a salvage pathway, where outside corrinoids are absorbed to make B12. Species from ... Woodson, Jesse D.; Reynolds, April A.; Escalante-Semerena, Jorge C. (2005). "ABC Transporter for Corrinoids in Halobacterium sp ... "CobA function is required for both de novo cobalamin biosynthesis and assimilation of exogenous corrinoids in Salmonella ...
4), the common corrinoid intermediate on the way to cobyric acid. At Harvard, the very same intermediate 2 was obtained around ... 2).: 1943-1948 The final steps from the common corrinoid intermediate E-37/HE-44 to cobyric acid E-44/HE-51 were carried out by ... 4 and 6 illustrate the atom, ring, and side chain enumeration in corrins: "Nomenclature of Corrinoids". Pure and Applied ... 4). The ETH group identified this totally synthetic corrinoid intermediate by direct comparison with a sample produced from ...
Matthews, R. G. (2009). "Cobalamin- and corrinoid-dependent enzymes". Metal Ions in Life Sciences. 6: 53-114. doi:10.1515/ ... A love affair with vitamins (2009) Cobalamin- and corrinoid-dependent enzymes Cobalamin-dependent and cobamide-dependent ...
Cracan, Valentin; Banerjee, Ruma (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". In Banci, Lucia (ed.). ...
Sato, Kazuyoshi; Shimizu, Shoichi; Fukui, Saburo (April 1970). "A cobalt-free corrinoid compound in Streptomyces olivaceus". ...
Cracan V, Banerjee R (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". In Banci L (ed.). Metallomics and ...
Cracan, Valentin; Banerjee, Ruma (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". In Banci, Lucia (ed.). ...
Cracan, Valentin; Banerjee, Ruma (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". In Banci, Lucia (ed.). ...
Cracan, Valentin; Banerjee, Ruma (2013). "Chapter 10 Cobalt and Corrinoid Transport and Biochemistry". In Banci, Lucia (ed.). ...
Upon deprotonation, the corrinoid ring is capable of binding cobalt. In vitamin B12, the resulting complex also features a ...
Santander PJ, Kajiwara Y, Williams HJ, Scott AI (February 2006). "Structural characterization of novel cobalt corrinoids ...
Maillard, J.; Schumacher, W.; Vazquez, F.; Regeard, C.; Hagen, W. R.; Holliger, C. (2003). "Characterization of the Corrinoid ...
Kovacs, Julie A. (2004-05-25). "Synthetic Analogues of Cysteinate-Ligated Non-Heme Iron and Non-Corrinoid Cobalt Enzymes". ... Her publications include: Synthetic analogues of cysteinate-ligated non-heme iron and non-corrinoid cobalt enzymes (DOI: ...
Maupin-Furlow, J.; Ferry, J.G. (1996). "Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron- ... Cobamide is a naturally occurring chemical compound containing cobalt in the corrinoid family of macrocyclic complexes. ... It is used for example in 5-methyltetrahydrosarcinapterin:corrinoid/iron-sulfur protein Co-methyltransferase. ...
Suh SJ, Escalante-Semerena JC (July 1993). "Cloning, sequencing and overexpression of cobA which encodes ATP:corrinoid ... This enzyme is also known as: Cobalamin adenosyltransferase ATP:cob(I)alamin adenosyltransferase ATP:corrinoid ... corrinoid adenosyltransferase) EC 2.5.1.17 is an enzyme which catalyses the conversion of cobalamin (vitamin B12) into one of ... corrinoid adenosyltransferase enzyme". J. Bacteriol. 186 (17): 5708-14. doi:10.1128/JB.186.17.5708-5714.2004. PMC 516830. PMID ...
A transfer of the methyl group from CH3-Tetrahydrofolate to the corrinoid protein requires the genes hgcA and hgcB . The methyl ... The Acetyl-CoA pathway for mercury methylation is done by sulfate reducing bacteria and is catalyzed by a corrinoid dependent ... group now on the corrinoid protein will then be transferred to mercury ion. This activity was shown to decrease in aerobic ...
The microorganisms may either be capable of de novo corrinoid biosynthesis or are dependent on exogenous vitamin B12. In humans ... "Pseudovitamin B12" refers to compounds that are corrinoids with a structure similar to the vitamin but without vitamin activity ... Pseudovitamin B12 is the majority corrinoid in spirulina, an algal health food sometimes erroneously claimed as having this ...
... is one of the rare enzyme types that use cobalt in a non-corrinoid manner. The mechanism by which the cobalt ... Nitrile hydratases (NHases; EC 4.2.1.84) are mononuclear iron or non-corrinoid cobalt enzymes that catalyse the hydration of ...
doi:10.1111/j.1574-6976.1998.tb00377.x. Glod G, Angst W, Holliger C, Schwarzenbach RP (1997). "Corrinoid-mediated reduction of ...
Most of these enzymes contain iron-sulfur (Fe-S) clusters, and a corrinoid cofactor at their active sites. Although the exact ...
"Sequence and transcript analysis of a novel Methanosarcina barkeri methyltransferase II homolog and its associated corrinoid ... coenzyme M methyltransferase of Methanosarcina barkeri catalyses both half-reactions of corrinoid-dependent dimethylsulfide: ...
... is believed that the ring is involved in positioning and displaying the methyl group of methylamine for attack by a corrinoid ... and exposing the methyl group derived from the methylamine to the binding cleft where it can interact with corrinoid. In this ...
Corrinoids at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "The Nomenclature of Corrinoids" at chem. ... Corrinoids are a group of compounds based on the skeleton of corrin, a cyclic system containing four pyrrole rings similar to ... Absorption of the corrinoid on a solid phase, allows detection of cyanide even in colored samples, rendering this method ... The binding of cyanide to the corrinoid cobalt center leads to a color change from orange to violet. Quantification of the ...
1G64: THE THREE-DIMENSIONAL STRUCTURE OF ATP:CORRINOID ADENOSYLTRANSFERASE FROM SALMONELLA TYPHIMURIUM. COBALAMIN/ATP TERNARY ...
The eutT Gene of Salmonella enterica Encodes an Oxygen-Labile, Metal-Containing ATP:Corrinoid Adenosyltransferase Enzyme. You ...
AH2 + ATP + 2 Co(II)-[methylamine-specific corrinoid protein] + H2O <=> A + ADP + 2 Co(I)-[methylamine-specific corrinoid ... AH2 + ATP + 2 Co(II)-[dimethylamine-specific corrinoid protein] + H2O <=> A + ADP + 2 Co(I)-[dimethylamine-specific corrinoid ... AH2 + ATP + 2 Co(II)-[trimethylamine-specific corrinoid protein] + H2O <=> A + ADP + 2 Co(I)-[trimethylamine-specific corrinoid ... Methyltrophic corrinoid proteins must have the cobalt atom in the active cobalt(I) state to become methylated. ...
Maupin-Furlow, J., & Ferry, J. G. (1996). Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron- ... Maupin-Furlow, Julie ; Ferry, James G. / Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron- ... Maupin-Furlow, J & Ferry, JG 1996, Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron-sulfur ... Dive into the research topics of Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron-sulfur ...
corrinoids. Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on ...
Categories: Corrinoids Image Types: Photo, Illustrations, Video, Color, Black&White, PublicDomain, CopyrightRestricted 3 images ...
The hydrophobic cobyrinic acid heptapropyl ester corrinoids XCbs-Pr (axial ligandX = CN-,SO32-,CH3- and CH3CH2-) have been ... Keywords : Hydrophobic vitamin B12; cobalt corrinoids; equilibrium constants; solvent polarity; trans influence. ...
Menon, S. and Ragsdale, S.W. (1998). Role of the [4Fe-4S] cluster in reductive activation of the cobalt center of the corrinoid ... Harder, S.R., Lu, W.P., Feinberg, B.A., and Ragsdale, S.W. (1989). Spectroelectrochemical studies of the corrinoid/iron-sulfur ... Nguyen, H.D., Studenik, S., and Diekert, G. (2013). Corrinoid activation by a RACE protein: studies on the interaction of the ... Methylation of CO dehydrogenase/acetyl-CoA synthase by the methylated corrinoid iron-sulfur protein. J. Biol. Chem. 274, 11513- ...
Bacterial OHR activity is supported by a plethora of other microorganisms that, with their activity, provide H2 and corrinoids ... Most of the RDases use corrinoids (coenzyme B12) as a cofactor [38,40]. It has been shown that 8.1-34 pg L−1 of cobalamin ... and Geobacter synthesize corrinoids [44,45,46,47,48,49]. Sulfate-reducing bacteria and methanogens could synthesize coenzyme B ...
Quantification of Corrinoids in Fermented Foods Michiko Taga Riparian fuel treatment effects on Alder, a critical species for ...
2.1.1.376 glycine betaine---corrinoid protein Co-methyltransferase. K25220 mtgB; glycine betaine---corrinoid protein Co- ... K25220 mtgB; glycine betaine---corrinoid protein Co-methyltransferase. Enzymes [BR:ko01000]. 2. Transferases. 2.1 Transferring ...
Genetic Analysis of Citrobacter sp.86 Reveals Involvement of Corrinoids in Chlordecone and Lindane Biotransformations. ...
PDB Compounds: (A:) 5-methyltetrahydrofolate corrinoid/iron sulfur protein methyltransferase. SCOPe Domain Sequences for d2e7fa ... PDB Description: 5-methyltetrahydrofolate corrinoid/iron sulfur protein methyltransferase complexed with methyltetrahydrofolate ...
CobW might be involved in cobalt reduction leading to cobalt(I) corrinoids. This entry represents the C-terminal domain found ... CobW might be involved in cobalt reduction leading to cobalt(I) corrinoids. ...
Rare plants that contain corrinoid compounds mostly comprise cobalamin analogues, which may compete with cobalamin (vitamin B12 ... In this study, vitamin B12 will be used to refer to all corrinoids exhibiting the qualitative biological activity of CN-B12 [2 ... To verify that the corrinoid detected by the bioassay was indeed a bioactive form of cobalamin, we used LC-MS/MS. The presence ... Background: Rare plants that contain corrinoid compounds mostly comprise cobalamin analogues, which may compete with cobalamin ...
40. Koyyalamudi SR, Jeong SC, Cho KY, Pang G. Vitamin B12 is the active corrinoid produced in cultivated white button mushrooms ...
Versatility in corrinoid salvaging and remodeling pathways supports corrinoid-dependent metabolism in Dehalococcoides mccartyi ... Sustainable growth of Dehalococcoides mccartyi 195 by corrinoid salvaging and remodeling in defined lactate-fermenting ... analyses reveal the structure and dynamics of a dechlorinating community containing Dehalococcoides mccartyi and corrinoid- ...
For more information, please visit: Biogeochemical Controls over Corrinoid Bioavailability to Organohalide-Respiring ... that can be used to recognize when the bioavailability corrinoids limits dechlorination activity. Using samples from Third ... and his research team are investigating the role of the microbial community for supplying specific nutrients called corrinoids ... The Effect of Corrinoid Co-factors on Bioremediation of Chlorinated Compounds. *Metabolic Interactions Supporting Effective TCE ...
... corrinoid adenosyltransferase from Lactobacillus reuteri complexed with cobalamin and ATP ... Structure of a F112A variant PduO-type ATP:corrinoid adenosyltransferase from Lactobacillus reuteri complexed with cobalamin ...
Co(II) methylated amine-specific corrinoid protein] reductase. Expasy is operated by the SIB Swiss Institute of Bioinformatics ...
Based on the predicted amino acid sequence, VC reductase is a novel member of the family of corrinoid/iron-sulfur cluster ...
Axial Ligation and Redox Changes at the Cobalt Ion in Cobalamin Bound to Corrinoid Iron-Sulfur Protein (Cofesp) or in Solution ...
The red-spotted ant mimic, Castianeria descripta, belongs to the corrinoid spider family Corinnidae. It ranges throughout the ...
Its full chemical name is cobalt(III) corrinoids, reflecting the fact that it contains a cobalt metal ion bound to a corrin ...
... considering that pure corrinoids can act as effective electron mediators [82]. Hypothetically, corrinoids in the slow ... 6). The enzymes encoded by pdgle and cbiQ are required for the transport of cobalt and the initial steps of corrinoid synthesis ... Men YJ, Seth EC, Yi S, Allen RH, Taga ME, Alvarez-Cohen L. Sustainable growth of Dehalococcoides mccartyi 195 by corrinoid ... The corrinoid cofactor of reductive dehalogenases affects dechlorination rates and extents in organohalide-respiring ...
Corrinoids:. Cyanocobalamin. Phycobilins:. Phycoerythrobilin , Phycocyanobilin , Phycourobilin , Phycoviolobilin. Porphyrins:. ...
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  • A solution of aquacyano-corrinoids, such as cobalamin or cobinamide, reacts with free cyanide in an aqueous sample. (wikipedia.org)
  • Background: Rare plants that contain corrinoid compounds mostly comprise cobalamin analogues, which may compete with cobalamin (vitamin B 12 (B 12 )) metabolism. (mdpi.com)
  • First identified in 1948, cobalamin is a red compound, containing a corrinoid ring (four pyrrole rings) with an atom of cobalt at its centre. (leanquick.org)
  • The binding of cyanide to the corrinoid cobalt center leads to a color change from orange to violet. (wikipedia.org)
  • Methyltrophic corrinoid proteins must have the cobalt atom in the active cobalt(I) state to become methylated. (expasy.org)
  • Because the cobalt(I)/cobalt(II) transformation has a very low redox potential the corrinoid cofactor is subject to adventitious oxidation to the cobalt(II) state, which renders the proteins inactive. (expasy.org)
  • CobW might be involved in cobalt reduction leading to cobalt(I) corrinoids. (embl-heidelberg.de)
  • Its full chemical name is cobalt(III) corrinoids, reflecting the fact that it contains a cobalt metal ion bound to a corrin ring. (colorwithleo.com)
  • Vitamin B12 is defined as a specific group of cobalt-containing corrinoids with biological activity in humans, also known as cobalamins. (ingrizo.com)
  • having a ebook Nomenclature of Corrinoids 1976 by amount and variation John Coulthart, editing talents, farmers and trusting words. (angliaobsolete.com)
  • Corrinoids are a group of compounds based on the skeleton of corrin, a cyclic system containing four pyrrole rings similar to porphyrins. (wikipedia.org)
  • Liquid chromatography-electrospray-ionization/tandem mass spectrometry analysis revealed that vitamin B 12 was the predominant corrinoid in the evaluated fish roe products examined, while no inactive corrinoid compounds were identified. (springer.com)
  • The CO dehydrogenase enzyme complex from Methanosarcina thermophila contains a corrinoid/iron-sulfur enzyme composed of two subunits (δ and γ). (psu.edu)
  • The putative CdhD and CdhE sequences are 37% identical to the sequences deduced from the genes encoding the β and α subunits of the corrinoid/iron- sulfur enzyme from Clostridium thermoaceticum. (psu.edu)
  • The CdhE sequence had a four- cysteine motif with the potential to bind a 4Fe-4S cluster previously identified in the corrinoid/iron-sulfur enzyme by electron paramagnetic resonance spectroscopy. (psu.edu)
  • Ferry, James G. / Characterization of the cdhD and cdhE genes encoding subunits of the corrinoid/iron-sulfur enzyme of the CO dehydrogenase complex from Methanosarcina thermophila . (psu.edu)
  • The hydrophobic cobyrinic acid heptapropyl ester corrinoids XCbs-Pr (axial ligandX = CN - ,SO 3 2- ,CH 3 - and CH 3 CH 2 - ) have been prepared from vitamin B 12 by hydrolysis of the amide side chains and their conversion to propyl esters. (scielo.org.za)
  • Cyanocobalamin is a vitamin of the B-complex family, commonly known as cobalamins (corrinoids). (godschosenministry.com)
  • Here we determine the mechanism of regulation in a riboswitch that responds to corrinoids-a family of coenzymes related to vitamin B12. (bvsalud.org)
  • The corrinoid riboswitch class, which responds to adenosylcobalamin (coenzyme B12) and related metabolites, is among the most widespread in bacteria. (bvsalud.org)
  • magadii also contained a set of genes that have been predicted to get involved in the conversion of cobyrinic acid into adenosylcobalamin, like a gene that's certain for the archaeal corrinoid salvage pathway. (others-signal.com)
  • Knowledge of these regulatory mechanisms allowed us to develop synthetic corrinoid riboswitches that convert repressing riboswitches to riboswitches that robustly induce gene expression in response to corrinoids. (bvsalud.org)
  • The team is designing and validating the B12-qChip - an innovative, high-throughput quantitative PCR tool - that can be used to recognize when the bioavailability corrinoids limits dechlorination activity. (clu-in.org)
  • At the University of Tennessee, Frank Loeffler, Ph.D., and his research team are investigating the role of the microbial community for supplying specific nutrients called corrinoids, which organohalide-respiring Dehalococcoidia require to dechlorinate and detoxify solvents such as tetrachloroethene (PCE) and trichloroethene (TCE). (clu-in.org)
  • Absorption of the corrinoid on a solid phase, allows detection of cyanide even in colored samples, rendering this method appropriate for the analysis of cyanide in water, wastewater, blood, and food. (wikipedia.org)
  • In both cases, mutually exclusive RNA secondary structures are responsible for promoting or preventing the formation of an intrinsic transcription terminator in response to the corrinoid binding state of the aptamer domain. (bvsalud.org)

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