UTP-Hexose-1-Phosphate Uridylyltransferase
UTP-Glucose-1-Phosphate Uridylyltransferase
UDPglucose-Hexose-1-Phosphate Uridylyltransferase
Galactosemias
Uridine Diphosphate Glucose
Hexoses
PII Nitrogen Regulatory Proteins
UDPglucose 4-Epimerase
Galactokinase
Molecular Sequence Data
Glutamate-Ammonia Ligase
Uridine Monophosphate
The biochemical role of glutamine 188 in human galactose-1-phosphate uridyltransferase. (1/99)
The substitution of arginine for glutamine at amino acid 188 (Q188R) ablates the function of human galactose-1-phosphate uridyltransferase (GALT) and is the most common mutation causing galactosemia in the white population. GALT catalyzes two consecutive reactions. The first reaction binds UDP-glucose (UDP-Glu), displaces glucose-1-phosphate (glu-1-P), and forms the UMP-GALT intermediate. In the second reaction, galactose-1-phosphate (gal-1-P) is bound, UDP-galactose (UDP-Gal) is released, and the free enzyme is recycled. In this study, we modeled glutamine, asparagine, and a common mutation arginine at amino acid 188 on the three-dimensional model of the Escherichia coli GALT-UMP protein crystal. We found that the amide group of the glutamine side chain could provide two hydrogen bonds to the phosphoryl oxygens of UMP with lengths of 2.52 and 2.82 A. Arginine and asparagine could provide only one hydrogen bond of 2. 52 and 3.02 A, respectively. To test this model, we purified recombinant human Gln188-, Arg188-, and Asn188-GALT and analyzed the first reaction in the absence of gal-1-P by quantitating glu-1-P released using enzyme-linked methods. Gln188-GALT displaced 80 +/- 7. 0 nmol glu-1-P/mg GALT/min in the first reaction. By contrast, both Arg188- and Asn188-GALT released more glu-1-P (170 +/- 8.0 and 129 +/- 28.4 nmol/mg GALT/min, respectively). The overall, double displacement reaction was quantitated in the presence of gal-1-P. Gln188-GALT produced 80,030 +/- 5,910 nmol glu-1-P/mg GALT/min, whereas the mutant Arg188- and Asn188-GALT released only 600 +/- 71. 2 and 2960 +/- 283.6 nmole glu-1-P/mg GALT/min, respectively. We conclude from these data that glutamine at position 188 stabilizes the UMP-GALT intermediate through hydrogen bonding and enables the double displacement of both glu-1-P and UDP-Gal. The substitution of arginine or asparagine at position 188 reduces hydrogen bonding and destabilizes UMP-GALT. The unstable UMP-GALT allows single displacement of glu-1-P with release of free GALT but impairs the subsequent binding of gal-1-P and displacement of UDP-Gal. (+info)Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers. (2/99)
Transferase-deficient galactosaemia, resulting from deficient activity of galactose-1-phosphate uridyltransferase (GALT), is relatively common among the Travellers, an endogamous group of commercial/industrial nomads within the Irish population. This study has estimated the incidence of classical transferase-deficient galactosaemia in Ireland and determined the underlying GALT mutation spectrum in the Irish population and in the Traveller group. Based upon a survey of newborn screening records, the incidence of classical transferase-deficient galactosaemia was estimated to be 1 in 480 and 1 in 30,000 among the Traveller and non-Traveller communities respectively. Fifty-six classical galactosaemic patients were screened for mutation in the GALT locus by standard molecular methods. Q188R was the sole mutant allele among the Travellers and the majority mutant allele among the non-Travellers (89.1%). Of the five non-Q188R mutant alleles in the non-Traveller group, one was R333G and one F194L with three remaining uncharacterized. Anonymous population screening has shown the Q188R carrier frequency to be 0.092 or 1 in 11 among the Travellers as compared with 0.009 or 1 in 107 among the non-Travellers. The Q188R mutation was shown to be in linkage disequilibrium with a Sac I RFLP flanking exon 6 of the GALT gene. This represents the first molecular genetic description of classical transferase-deficient galactosaemia in Ireland and raises intriguing questions concerning the genetic history of the Irish Travellers. (+info)Expression of human inositol monophosphatase suppresses galactose toxicity in Saccharomyces cerevisiae: possible implications in galactosemia. (3/99)
A suppressor of galactose toxicity in a gal7 yeast strain (lacking galactose 1-phosphate uridyl transferase) has been isolated from a HeLa cell cDNA library. Analysis of the plasmid clone indicated that the insert has an ORF identical to that of hIMPase (human myo-inositol monophosphatase). The ability of hIMPase to suppress galactose toxicity is sensitive to the presence of Li(+) in the medium. A gal7 yeast strain harboring a plasmid containing cloned hIMPase grows on galactose as a sole carbon source. hIMPase mediated galactose metabolism is dependent on the functionality of GAL1 as well as GAL10 encoded galactokinase and epimerase respectively. These results predicted that the UDP-glucose/galactose pyrophosphorylase mediated pathway may be responsible for the relief of galactose toxicity. Experiments conducted to test this prediction revealed that expression of UGP1 encoded UDP-glucose pyrophosphorylase can indeed overcome the relief of galactose toxicity. Moreover, expression of UGP1 allows a gal7 strain to grow on galactose as a sole carbon source. Unlike the hIMPase mediated relief of galactose toxicity, UGP1 mediated relief of galactose toxicity is lithium insensitive. Based on our results and on the basis of available information on galactose toxicity, we suggest an alternative explanation for the molecular mechanism of galactose toxicity. (+info)Molecular basis for phenotypic heterogeneity in galactosaemia: prediction of clinical phenotype from genotype in Japanese patients. (4/99)
We identified 14 mutations in 15 Japanese subjects from 13 families with galactose-1-phosphate uridyltransferase (GALT) deficiency using denaturing gradient gel electrophoresis (DGGE) and direct sequence analysis. These mutations accounted for 22 (96%) of 23 mutant alleles in 15 Japanese subjects. The mutational spectrum included nine missense mutations (M142V, G179D, A199T, R231H, W249R, N314D, P325L, R333Q, and R333W), two deletions (L275fsdelT and Q317fsdelC), a nonsense mutation (W249X), and two splicing mutations (V85-N97fsdel38bp and IVS4nt+1). Ten of the 14 mutations have not been reported in Caucasians. Differences in frequency and spectrum of GALT mutations suggest that the mutations may have occurred after racial divergence of Caucasians and Asians. The Duarte variant in Japanese was associated with the N314D mutation, g.1105G > C, g.1323G > A, and g.1391G > A (SacI -) polymorphisms, as in Caucasians. The Duarte variant may have occurred before racial divergence, and was an ancient mutation. In vitro GALT activities of nine missense mutations were determined by a COS cell expression system, and indicated between 1.3% and 35% of wild-type control. Patients with R333Q (29% in vitro GALT activity) or A199T (35%) showed mild clinical phenotypes, i.e. no ovarian failure or neurological deterioration. Genotype determination is useful for predicting biochemical and clinical phenotypes in classic galactosaemia, and can be of further help in managing patients with this disorder. (+info)A case-control study of galactose consumption and metabolism in relation to ovarian cancer. (5/99)
Consumption or metabolism of dairy sugar and ovarian cancer have been linked based on evidence that galactose may be toxic to ovarian germ cells and that ovarian cancer is induced in animals by depletion of oocytes. We assessed consumption of dairy products and obtained blood for biochemical and molecular genetic assessment of galactose metabolism in 563 women with newly diagnosed epithelial ovarian cancer and 523 control women selected either by random digit dialing or through lists of residents in eastern Massachusetts and New Hampshire. We observed no significant differences between cases and controls in usual consumption of various types of dairy products or total daily lactose (the principal source of galactose in the diet); nor did we find that RBC activity of either galactose-1-phosphate uridyl transferase (GALT) or galactokinase differed. The mean (and SE) activity of uridine diphospho-galactose 4'-epimerase (in micromoles per hour per gram of hemoglobin) was, however, significantly lower (P < 0.005) in cases compared with controls, 20.32 (0.31) versus 21.64 (0.36). Ovarian cancer cases were also more likely to carry the N314D polymorphism of the GALT gene, generally predisposing to lower GALT activity. The difference was most evident for endometrioid and clear cell types of ovarian cancer, in which 3.9% of cases were found to be homozygous for N314D compared with 0.4% of controls, yielding an odds ratio and 95% confidence interval of 14.17 (2.62-76.60). We conclude that, whereas adult consumption of lactose carries no clear risk for the disease, certain genetic or biochemical features of galactose metabolism may influence disease risk for particular types of ovarian cancer. (+info)Functional consequence of substitutions at residue 171 in human galactose-1-phosphate uridylyltransferase. (6/99)
Impairment of the human enzyme galactose-1-phosphate uridylyltransferase (hGALT) results in the potentially lethal disorder classic galactosemia. Although a variety of naturally occurring mutations have been identified in patient alleles, few have been well characterized. We have explored the functional significance of a common patient mutation, F171S, using a strategy of conservative substitution at the defined residue followed by expression of the wild-type and, alternatively, substituted proteins in a null-background strain of yeast. As expected from patient studies, the F171S-hGALT protein demonstrated <0.1% wild-type levels of activity, although two of three conservatively substituted moieties, F171L- and F171Y-hGALT, demonstrated approximately 10% and approximately 4% activity, respectively. The third protein, F171W, demonstrated severely reduced abundance, precluding further study. Detailed kinetic analyses of purified wild-type, F171L- and F171Y-hGALT enzymes, coupled with homology modeling of these proteins, enabled us to suggest that the effects of these substitutions resulted largely from altering the position of a catalytically important residue, Gln-188, and secondarily, by altering the subunit interface and perturbing hexose binding to the uridylylated enzyme. These results not only provide insight into the functional impact of a single common patient allele and offer a paradigm for similar studies of other clinically or biochemically important residues, but they further help to elucidate activity of the wild-type human GALT enzyme. (+info)'Durate variant with clinical signs' has alpha1 -antitrypsin genotype ZZ. (7/99)
A patient with neonatal jaundice and cirrhosis who was previously reported homozygous for the Durate variant of galactose-1-phosphate uridyl transferase has the ZZ genotype for alpha1-antitrypsin. A sister of the patient, also with ZZ genotype, is less severly affected with liver disease and is a heterozygote for the Durate variant. Since a number of patients with ZZ genotype of alpha1-antitrypsin have been previously reported to have liver disease, the latter genotype is the more probable explanation for the patients' clinical state. A question is raised, however, whether the Duarte variant may be specifically associated with the development of liver disease in ZZ individuals. (+info)Quantitative Beutler test for newborn mass screening of galactosemia using a fluorometric microplate reader. (8/99)
BACKGROUND: The Beutler enzyme spot test is an effective assay for newborn mass screening of galactosemia, but it is qualitative and relies on visual interpretation. We describe a quantitative, instrumental modification of the assay. METHODS: We modified the macroscopic visual Beutler enzyme spot test by adding extraction of blood components from filter paper, deproteinization with acetone-methanol, and quantification and recording by a fluorescent microplate reader and personal computer. All handling was performed in microplates. The measurement time was 90 min. RESULTS: Fluorescence intensity (FI) of healthy controls correlated with hematocrit and galactose-1-phosphate uridyltransferase (GALT) activity. Patients with GALT deficiency were distinguished clearly from healthy subjects and heterozygous carriers by FI. FI decreased to 75% of the initial activity after storage at 25 degrees C for 3 days and to 40% after storage at 37 degrees C for 7 days. Screening of 46 742 newborns yielded 1 false-positive result (in a heterozygous carrier), 1 patient with glucose-6-phosphate dehydrogenase deficiency, and no apparent false negatives as judged by concurrent measurements of galactose and galactose-1-phosphate. CONCLUSIONS: The quantitative Beutler test can provide precise GALT activity in newborn mass screening, and can take into consideration the influence of high temperature and humidity, duration between sampling and testing, and anemia. This method is clinically useful, simple, automated, and highly reliable for newborn mass screening of galactosemia. (+info)UTP-hexose-1-phosphate uridylyltransferase is an enzyme that catalyzes the transfer of a uridine monophosphate (UMP) group from a uridine triphosphate (UTP) molecule to a hexose-1-phosphate molecule, forming a UDP-hexose molecule. This reaction is an essential step in the biosynthesis of various glycosylated compounds, including glycoproteins and polysaccharides.
The systematic name for this enzyme is UTP:alpha-D-hexose-1-phosphate uridylyltransferase. It is also known as UDP-glucose pyrophosphorylase, which is a more specific name that refers to the formation of UDP-glucose from glucose-1-phosphate and UTP.
The enzyme plays a crucial role in carbohydrate metabolism and has been implicated in several diseases, including diabetes and cancer. Inhibitors of this enzyme have been explored as potential therapeutic agents for the treatment of these conditions.
UTP-Glucose-1-Phosphate Uridylyltransferase is an enzyme that catalyzes the reaction to form UDP-glucose from UTP and glucose-1-phosphate. This reaction plays a crucial role in the biosynthesis of various carbohydrates, glycoproteins, and glycolipids in the body. The enzyme is also known as UDP-glucose pyrophosphorylase or simply as UGPase.
The systematic name for this enzyme is glucose-1-phosphate:UTP uridylyltransferase, and its reaction can be represented as follows:
UTP + glucose-1-phosphate ⇌ UDP-glucose + pyrophosphate
The enzyme is widely distributed in nature and is found in various organisms, including bacteria, plants, and animals. In humans, UGPase is present in multiple tissues, such as the liver, kidney, and brain. Defects in this enzyme can lead to several metabolic disorders, highlighting its importance in maintaining normal bodily functions.
UDP-glucose-hexose-1-phosphate uridylyltransferase is an enzyme that plays a role in the metabolism of carbohydrates. The systematic name for this enzyme is UDP-glucose:alpha-D-hexose-1-phosphate uridylyltransferase.
This enzyme catalyzes the following reaction:
UDP-glucose + alpha-D-hexose 1-phosphate glucose 1-phosphate + UDP-alpha-D-hexose
In simpler terms, this enzyme helps to transfer a uridylyl group (UDP) from UDP-glucose to another hexose sugar that is attached to a phosphate group. This reaction allows for the interconversion of different sugars in the cell and plays a role in various metabolic pathways, including the synthesis of glycogen and other complex carbohydrates.
Deficiencies or mutations in this enzyme can lead to various genetic disorders, such as congenital disorder of glycosylation type IIb (CDGIIb) and polycystic kidney disease.
Galactosemia is a rare metabolic disorder that affects the body's ability to metabolize the simple sugar galactose, which is found in milk and other dairy products. It is caused by deficiency or complete absence of one of the three enzymes needed to convert galactose into glucose:
1. Galactokinase (GALK) deficiency - also known as Galactokinase galactosemia, is a milder form of the disorder.
2. Galactose-1-phosphate uridylyltransferase (GALT) deficiency - the most common and severe form of classic galactosemia.
3. Galactose epimerase (GALE) deficiency - also known as Epimerase deficiency galactosemia, is a rare and milder form of the disorder.
The most severe form of the disorder, GALT deficiency, can lead to serious health problems such as cataracts, liver damage, mental retardation, and sepsis if left untreated. Treatment typically involves removing galactose from the diet, which requires avoiding all milk and dairy products. Early diagnosis and treatment are crucial for improving outcomes in individuals with galactosemia.
I'm sorry for any confusion, but "galactosephosphates" is not a widely recognized or established term in medicine or biochemistry. It seems that this term may be a combination of "galactose," which is a simple sugar, and "phosphate," which is a common ion found in biological systems. However, without more context, it's difficult to provide an accurate medical definition for this term.
Galactose is a monosaccharide that is metabolized in the body through the Leloir pathway, and defects in this pathway can lead to genetic disorders such as galactosemia. Phosphates are often found in biological molecules, including nucleic acids (DNA and RNA) and certain sugars (like glucose-1-phosphate).
Without further context or information about how "galactosephosphates" is being used, I would be cautious about assuming that it refers to a specific medical concept or condition.
Nucleotidyltransferases are a class of enzymes that catalyze the transfer of nucleotides to an acceptor molecule, such as RNA or DNA. These enzymes play crucial roles in various biological processes, including DNA replication, repair, and recombination, as well as RNA synthesis and modification.
The reaction catalyzed by nucleotidyltransferases typically involves the donation of a nucleoside triphosphate (NTP) to an acceptor molecule, resulting in the formation of a phosphodiester bond between the nucleotides. The reaction can be represented as follows:
NTP + acceptor → NMP + pyrophosphate
where NTP is the nucleoside triphosphate donor and NMP is the nucleoside monophosphate product.
There are several subclasses of nucleotidyltransferases, including polymerases, ligases, and terminases. These enzymes have distinct functions and substrate specificities, but all share the ability to transfer nucleotides to an acceptor molecule.
Examples of nucleotidyltransferases include DNA polymerase, RNA polymerase, reverse transcriptase, telomerase, and ligase. These enzymes are essential for maintaining genome stability and function, and their dysregulation has been implicated in various diseases, including cancer and neurodegenerative disorders.
Uridine Diphosphate Glucose (UDP-glucose) is a nucleotide sugar that plays a crucial role in the synthesis and metabolism of carbohydrates in the body. It is formed from uridine triphosphate (UTP) and glucose-1-phosphate through the action of the enzyme UDP-glucose pyrophosphorylase.
UDP-glucose serves as a key intermediate in various biochemical pathways, including glycogen synthesis, where it donates glucose molecules to form glycogen, a large polymeric storage form of glucose found primarily in the liver and muscles. It is also involved in the biosynthesis of other carbohydrate-containing compounds such as proteoglycans and glycolipids.
Moreover, UDP-glucose is an essential substrate for the enzyme glucosyltransferase, which is responsible for adding glucose molecules to various acceptor molecules during the process of glycosylation. This post-translational modification is critical for the proper folding and functioning of many proteins.
Overall, UDP-glucose is a vital metabolic intermediate that plays a central role in carbohydrate metabolism and protein function.
Hexoses are simple sugars (monosaccharides) that contain six carbon atoms. The most common hexoses include glucose, fructose, and galactose. These sugars play important roles in various biological processes, such as serving as energy sources or forming complex carbohydrates like starch and cellulose. Hexoses are essential for the structure and function of living organisms, including humans.
PII nitrogen regulatory proteins are a type of signal transduction protein involved in the regulation of nitrogen metabolism in bacteria and archaea. They are named "PII" because they contain two identical subunits, each with a molecular weight of approximately 12 kilodaltons. These proteins play a crucial role in sensing and responding to changes in the energy status and nitrogen availability within the cell.
The PII protein is composed of three domains: the T-domain, which binds ATP and ADP; the N-domain, which binds 2-oxoglutarate (an indicator of carbon and nitrogen status); and the B-domain, which is involved in signal transduction. The PII protein can exist in different conformational states depending on whether it is bound to ATP or ADP, and this affects its ability to interact with downstream effectors.
One of the primary functions of PII proteins is to regulate the activity of glutamine synthetase (GS), an enzyme that catalyzes the conversion of glutamate to glutamine. When nitrogen is abundant, PII proteins bind to GS and stimulate its activity, promoting the assimilation of ammonia into organic compounds. Conversely, when nitrogen is scarce, PII proteins dissociate from GS, allowing it to be inhibited by other regulatory proteins.
PII proteins can also interact with other enzymes and regulators involved in nitrogen metabolism, such as nitrogenase, uridylyltransferase/uridylyl-removing enzyme (UT/UR), and transcriptional regulators. Through these interactions, PII proteins help to coordinate the cell's response to changes in nitrogen availability and energy status, ensuring that resources are allocated efficiently and effectively.
UDP-glucose 4-epimerase (UGE) is an enzyme that catalyzes the reversible interconversion of UDP-galactose and UDP-glucose, two important nucleotide sugars involved in carbohydrate metabolism. This enzyme plays a crucial role in maintaining the balance between these two molecules, which are essential for the synthesis of various glycoconjugates, such as glycoproteins and proteoglycans. UGE is widely distributed in nature and has been identified in various organisms, including humans. In humans, deficiency or mutations in this enzyme can lead to a rare genetic disorder known as galactosemia, which is characterized by an impaired ability to metabolize the sugar galactose, resulting in several health issues.
Phosphates, in a medical context, refer to the salts or esters of phosphoric acid. Phosphates play crucial roles in various biological processes within the human body. They are essential components of bones and teeth, where they combine with calcium to form hydroxyapatite crystals. Phosphates also participate in energy transfer reactions as phosphate groups attached to adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Additionally, they contribute to buffer systems that help maintain normal pH levels in the body.
Abnormal levels of phosphates in the blood can indicate certain medical conditions. High phosphate levels (hyperphosphatemia) may be associated with kidney dysfunction, hyperparathyroidism, or excessive intake of phosphate-containing products. Low phosphate levels (hypophosphatemia) might result from malnutrition, vitamin D deficiency, or certain diseases affecting the small intestine or kidneys. Both hypophosphatemia and hyperphosphatemia can have significant impacts on various organ systems and may require medical intervention.
Galactokinase is a medical/biochemical term that refers to the enzyme responsible for the first step in the metabolic pathway of galactose, a simple sugar or monosaccharide. This enzyme catalyzes the phosphorylation of D-galactose to form D-galactose 1-phosphate, using ATP as the phosphate donor.
Galactokinase is a crucial enzyme in the metabolism of lactose and other galactose-containing carbohydrates. Deficiency or mutation in this enzyme can lead to a genetic disorder called Galactokinase Deficiency, which results in the accumulation of galactose and its derivatives in body tissues, potentially causing cataracts and other symptoms associated with galactosemia.
Molecular sequence data refers to the specific arrangement of molecules, most commonly nucleotides in DNA or RNA, or amino acids in proteins, that make up a biological macromolecule. This data is generated through laboratory techniques such as sequencing, and provides information about the exact order of the constituent molecules. This data is crucial in various fields of biology, including genetics, evolution, and molecular biology, allowing for comparisons between different organisms, identification of genetic variations, and studies of gene function and regulation.
Glutamate-ammonia ligase, also known as glutamine synthetase, is an enzyme that plays a crucial role in nitrogen metabolism. It catalyzes the formation of glutamine from glutamate and ammonia in the presence of ATP, resulting in the conversion of ammonia to a less toxic form. This reaction is essential for maintaining nitrogen balance in the body and for the synthesis of various amino acids, nucleotides, and other biomolecules. The enzyme is widely distributed in various tissues, including the brain, liver, and muscle, and its activity is tightly regulated through feedback inhibition by glutamine and other metabolites.
Uridine Monophosphate (UMP) is a nucleotide that is a constituent of RNA (Ribonucleic Acid). It consists of a nitrogenous base called Uridine, linked to a sugar molecule (ribose) and a phosphate group. UMP plays a crucial role in various biochemical reactions within the body, including energy transfer and cellular metabolism. It is also involved in the synthesis of other nucleotides and serves as an important precursor in the production of genetic material during cell division.
RNA nucleotidyltransferases are a class of enzymes that catalyze the template-independent addition of nucleotides to the 3' end of RNA molecules, using nucleoside triphosphates as substrates. These enzymes play crucial roles in various biological processes, including RNA maturation, quality control, and regulation.
The reaction catalyzed by RNA nucleotidyltransferases involves the formation of a phosphodiester bond between the 3'-hydroxyl group of the RNA substrate and the alpha-phosphate group of the incoming nucleoside triphosphate. This results in the elongation of the RNA molecule by one or more nucleotides, depending on the specific enzyme and context.
Examples of RNA nucleotidyltransferases include poly(A) polymerases, which add poly(A) tails to mRNAs during processing, and terminal transferases, which are involved in DNA repair and V(D)J recombination in the immune system. These enzymes have been implicated in various diseases, including cancer and neurological disorders, making them potential targets for therapeutic intervention.
