Vitamin B 12
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.
Binding of Cob(II)alamin to the adenosylcobalamin-dependent ribonucleotide reductase from Lactobacillus leichmannii. Identification of dimethylbenzimidazole as the axial ligand. (1/283)
The ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii catalyzes the reduction of nucleoside 5'-triphosphates to 2'-deoxynucleoside 5'-triphosphates and uses coenzyme B12, adenosylcobalamin (AdoCbl), as a cofactor. Use of a mechanism-based inhibitor, 2'-deoxy-2'-methylenecytidine 5'-triphosphate, and isotopically labeled RTPR and AdoCbl in conjunction with EPR spectroscopy has allowed identification of the lower axial ligand of cob(II)alamin when bound to RTPR. In common with the AdoCbl-dependent enzymes catalyzing irreversible heteroatom migrations and in contrast to the enzymes catalyzing reversible carbon skeleton rearrangements, the dimethylbenzimidazole moiety of the cofactor is not displaced by a protein histidine upon binding to RTPR. (+info)The reaction of the substrate analog 2-ketoglutarate with adenosylcobalamin-dependent glutamate mutase. (2/283)
Glutamate mutase is one of several adenosylcobalamin-dependent enzymes that catalyze unusual rearrangements that proceed through a mechanism involving free radical intermediates. The enzyme exhibits remarkable specificity, and so far no molecules other than L-glutamate and L-threo-3-methylaspartate have been found to be substrates. Here we describe the reaction of glutamate mutase with the substrate analog, 2-ketoglutarate. Binding of 2-ketoglutarate (or its hydrate) to the holoenzyme elicits a change in the UV-visible spectrum consistent with the formation of cob(II)alamin on the enzyme. 2-ketoglutarate undergoes rapid exchange of tritium between the 5'-position of the coenzyme and C-4 of 2-ketoglutarate, consistent with the formation of a 2-ketoglutaryl radical analogous to that formed with glutamate. Under aerobic conditions this leads to the slow inactivation of the enzyme, presumably through reaction of free radical species with oxygen. Despite the formation of a substrate-like radical, no rearrangement of 2-ketoglutarate to 3-methyloxalacetate could be detected. The results indicate that formation of the C-4 radical of 2-ketoglutarate is a facile process but that it does not undergo further reactions, suggesting that this may be a useful substrate analog with which to investigate the mechanism of coenzyme homolysis. (+info)Methanol:coenzyme M methyltransferase from Methanosarcina barkeri -- substitution of the corrinoid harbouring subunit MtaC by free cob(I)alamin. (3/283)
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)Adenosylcobalamin-mediated methyl transfer by toluate cis-dihydrodiol dehydrogenase of the TOL plasmid pWW0. (4/283)
We identified and characterized a methyl transfer activity of the toluate cis-dihydrodiol (4-methyl-3,5-cyclohexadiene-cis-1, 2-diol-1-carboxylic acid) dehydrogenase of the TOL plasmid pWW0 towards toluene cis-dihydrodiol (3-methyl-4,5-cyclohexadiene-cis-1, 2-diol). When the purified enzyme from the recombinant Escherichia coli containing the xylL gene was incubated with toluene cis-dihydrodiol in the presence of NAD+, the end products differed depending on the presence of adenosylcobalamin (coenzyme B12). The enzyme yielded catechol in the presence of adenosylcobalamin, while it gave 3-methylcatechol in the absence of the cofactor. Adenosylcobalamin was transformed to methylcobalamin as a result of the enzyme reaction, which indicates that the methyl group of the substrate was transferred to adenosylcobalamin. Other derivatives of the cobalamin such as aquo (hydroxy)- and cyanocobalamin did not mediate the methyl transfer reaction. The dehydrogenation and methyl transfer reactions were assumed to occur concomitantly, and the methyl transfer reaction seemed to depend on the dehydrogenation. To our knowledge, the enzyme is the first dehydrogenase that shows a methyl transfer activity as well. (+info)Co-ordinate variations in methylmalonyl-CoA mutase and methionine synthase, and the cobalamin cofactors in human glioma cells during nitrous oxide exposure and the subsequent recovery phase. (5/283)
We investigated the co-ordinate variations of the two cobalamin (Cbl)-dependent enzymes, methionine synthase (MS) and methylmalonyl-CoA mutase (MCM), and measured the levels of their respective cofactors, methylcobalamin (CH3Cbl) and adenosylcobalamin (AdoCbl) in cultured human glioma cells during nitrous oxide exposure and during a subsequent recovery period of culture in a nitrous oxide-free atmosphere (air). In agreement with published data, MS as the primary target of nitrous oxide was inactivated rapidly (initial rate of 0.06 h(-1)), followed by reduction of CH3Cbl (to <20%). Both enzyme activity and cofactor levels recovered rapidly when the cells were subsequently cultured in air, but the recovery was completely blocked by the protein-synthesis inhibitor, cycloheximide. During MS inactivation, there was a reduction of cellular AdoCbl and holo-MCM activity (measured in the absence of exogenous AdoCbl) to about 50% of pre-treatment levels. When the cells were transferred to air, both AdoCbl and holo-MCM activity recovered, albeit more slowly than the MS system. Notably, the regain of the holo-MCM and AdoCbl was enhanced rather than inhibited by cycloheximide. These findings confirm irreversible damage of MS by nitrous oxide; hence, synthesis of the enzyme is required to restore its activity. In contrast, restoration of holo-MCM activity is only dependent on repletion of the AdoCbl cofactor. We also observed a synchronous fluctuation in AdoCbl and the much larger hydroxycobalamin pool during the inactivation and recovery phase, suggesting that the loss and repletion of AdoCbl reflect changes in intracellular Cbl homoeostasis. Our data demonstrate that the nitrous oxide-induced changes in MS and CH3Cbl are associated with reversible changes in both MCM holoactivity and the AdoCbl level, suggesting co-ordinate distribution of Cbl cofactors during depletion and repletion. (+info)Identification and expression of the genes encoding a reactivating factor for adenosylcobalamin-dependent glycerol dehydratase. (6/283)
Adenosylcobalamin-dependent glycerol dehydratase undergoes inactivation by glycerol, the physiological substrate, during catalysis. In permeabilized cells of Klebsiella pneumoniae, the inactivated enzyme is reactivated in the presence of ATP, Mg2+, and adenosylcobalamin. We identified the two open reading frames as the genes for a reactivating factor for glycerol dehydratase and designated them gdrA and gdrB. The reactivation of the inactivated glycerol dehydratase by the gene products was confirmed in permeabilized recombinant Escherichia coli cells coexpressing GdrA and GdrB proteins with glycerol dehydratase. (+info)Structure and dynamics of the B12-binding subunit of glutamate mutase from Clostridium cochlearium. (7/283)
Glutamate mutase (Glm) is an adenosylcobamide-dependent enzyme that catalyzes the reversible rearrangement of (2S)-glutamate to (2S, 3S)-3-methylaspartate. The active enzyme from Clostridium cochlearium consists of two subunits (of 53.6 and 14.8 kDa) as an alpha2beta2 tetramer, whose assembly is mediated by coenzyme B12. The smaller of the protein components, GlmS, has been suggested to be the B12-binding subunit. Here we report the solution structure of GlmS, determined from a heteronuclear NMR-study, and the analysis of important dynamical aspects of this apoenzyme subunit. The global fold and dynamic behavior of GlmS in solution are similar to those of the corresponding subunit MutS from C. tetanomorphum, which has previously been investigated using NMR-spectroscopy. Both solution structures of the two Glm B12-binding subunits share striking similarities with that determined by crystallography for the B12-binding domain of methylmalonyl CoA mutase (Mcm) from Propionibacterium shermanii, which is B12 bound. In the crystal structure a conserved histidine residue was found to be coordinated to cobalt, displacing the endogenous axial ligand of the cobamide. However, in GlmS and MutS the sequence motif, Asp-x-His-x-x-Gly, which includes the cobalt-coordinating histidine residue, and a predicted alpha-helical region following the motif, are present as an unstructured and highly mobile loop. In the absence of coenzyme, the B12-binding site apparently is only partially formed. By comparing the crystal structure of Mcm with the solution structures of B12-free GlmS and MutS, a consistent picture on the mechanism of B12 binding has been obtained. Important elements of the binding site only become structured upon binding B12; these include the cobalt-coordinating histidine residue, and an alpha helix that forms one side of the cleft accommodating the nucleotide 'tail' of the coenzyme. (+info)Isolation of acetate auxotrophs of the methane-producing archaeon Methanococcus maripaludis by random insertional mutagenesis. (8/283)
To learn more about autotrophic growth of methanococci, we isolated nine conditional mutants of Methanococcus maripaludis after transformation of the wild type with a random library in pMEB.2, a suicide plasmid bearing the puromycin-resistance cassette pac. These mutants grew poorly in mineral medium and required acetate or complex organic supplements such as yeast extract for normal growth. One mutant, JJ104, was a leaky acetate auxotroph. A plasmid, pWDK104, was recovered from this mutant by electroporation of a plasmid preparation into Escherichia coli. Transformation of wild-type M. maripaludis with pWDK104 produced JJ104-1, a mutant with the same phenotype as JJ104, thus establishing that insertion of pWDK104 into the genome was responsible for the phenotype. pWDK104 contained portions of the methanococcal genes encoding an ABC transporter closely related to MJ1367-MJ1368 of M. jannaschii. Because high levels of molybdate, tungstate, and selenite restored growth to wild-type levels, this transporter may be specific for these oxyanions. A second acetate auxotroph, JJ117, had an absolute growth requirement for either acetate or cobalamin, and wild-type growth was observed only in the presence of both. Cobinamide, 5', 6'-dimethylbenzimidazole, and 2-aminopropanol did not replace cobalamin. This phenotype was correlated with tandem insertions in the genome but not single insertions and appeared to have resulted from an indirect effect on cobamide metabolism. Plasmids rescued from other mutants contained portions of ORFs denoted in M. jannaschii as endoglucanase (MJ0555), transketolase (MJ0681), thiamine biosynthetic protein thiI (MJ0931), and several hypothetical proteins (MJ1031, MJ0835, and MJ0835.1). (+info)Identification and expression of the genes encoding a reactivating factor for adenosylcobalamin-dependent glycerol dehydratase<...
RCSB PDB
- 1C9K: THE THREE DIMENSIONAL STRUCTURE OF ADENOSYLCOBINAMIDE KINASE/ ADENOSYLCOBINAMIDE PHOSPHATE...
Thermolysis of coenzymes B12 at physiological temperatures: activation parameters for cobalt-carbon bond homolysis and a...
This Week in Science | Science
Sequence Similarity
- 1JHA: Structural Investigation of the Biosynthesis of Alternative Lower Ligands for Cobamides...
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Designated organic active ingredient containing (doai) > Ester doai > Z-c(=o)-o-y wherein z is hydrogen or an organic radical...
cob(II)alamin reductase - oi
ENZYME entry 5.4.99.61
NWMN RS11195 - AureoWiki
cobalt-precorrin-5B (C1)-methyltransferase(EC 2.1.1.195) - Creative Enzymes
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Publicaţii
Structures of the human GTPase MMAA and vitamin B12-dependent methylmalonyl-CoA mutase and insight into their complex formation...
Evidence for axial coordination of 5,6-dimethylbenzimidazole to the cobalt atom of adenosylcobalamin bound to diol dehydratase<...
One pathway can incorporate either adenine or dimethylbenzimidazole as an α-axial ligand of B<sub>12</sub> cofactors in...
The mechanism of action of coenzyme B12. I: Mechanism of action of coenzyme B12. Hydrogen transfer in the isomerization of beta...
Generation and reactions of organic radical cations in zeolites<...
B12 Liquid
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Adsorption and Organization of the Organic Radical 3-Carboxyproxyl on a Cu(110) Surface : A Combined STM, RAIRS, and DFT Study
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ENZYME entry 2.4.2.21
400 தொண்டர்களுக்கு ஆண்மையிழப்பு சிகிச்சை- குர்மீத்துக்கு சி.பி.ஐ கிடுக்கிப்பிடி! | CBI questions Ram Rahim on forced...
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Vitamin B12
Perlman D (1959). "Microbial synthesis of cobamides". Advances in Applied Microbiology. 1: 87-122. doi:10.1016/S0065-2164(08) ...
Cobalamin biosynthesis
Perlman D (1959). "Microbial synthesis of cobamides". Advances in Applied Microbiology. 1: 87-122. doi:10.1016/S0065-2164(08) ...
Ribonucleoside-triphosphate reductase
Blakley RL (May 1965). "Cobamides and ribonucleotide reduction. I. Cobamide stimulation of ribonucleotide reduction in extracts ...
5-Aminoimidazole ribotide
Sokolovskaya, Olga M.; Shelton, Amanda N.; Taga, Michiko E. (2020). "Sharing vitamins: Cobamides unveil microbial interactions ...
Nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase
"Structural investigation of the biosynthesis of alternative lower ligands for cobamides by nicotinate mononucleotide: 5,6- ...
List of MeSH codes (D03)
... cobamides MeSH D03.383.129.578.840.437.777.560 - hydroxocobalamin MeSH D03.383.129.578.840.500 - porphyrins MeSH D03.383. ... cobamides MeSH D03.549.909.437.777.560 - hydroxocobalamin MeSH D03.549.909.500 - porphyrins MeSH D03.549.909.500.250 - ...
List of MeSH codes (D04)
... cobamides MeSH D04.345.783.437.777.560 - hydroxocobalamin MeSH D04.345.783.500 - porphyrins MeSH D04.345.783.500.250 - ...
KEGG ENZYME: 2.4.2.55
MH DELETED MN ADDED MN
B12 deficiency: a silent epidemic with serious consequences
DeCS
Cobamides Entry term(s). B12 Coenzymes, Vitamin Coenzymes, Vitamin B12 Deoxyadenosinecobalamins Vitamin B 12 Coenzymes Vitamin ... deficiency: coordinate COBAMIDES /defic (IM) with VITAMIN B 12 DEFICIENCY (IM). Allowable Qualifiers:. AA analogs & derivatives ... Cobamides Entry term(s):. B12 Coenzymes, Vitamin. Coenzymes, Vitamin B12. Deoxyadenosinecobalamins. Vitamin B 12 Coenzymes. ... Cobamides - Preferred Concept UI. M0004665. Preferred term. ...
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Akkermansia/genética
Cobamides have structural variability in the lower ligand, and selectivity for particular cobamides has been observed in most ... However, A. muciniphila MucT is unable to synthesize cobamides de novo, and the specific forms that can be used by A. ... We found that the levels of growth of A. muciniphila MucT were nearly identical with each of seven cobamides tested, in ... A. muciniphila strain MucT is known to use cobamides, the vitamin B12 family of cofactors with structural diversity in the ...
A model to study vitamin B12 form, function and deficiency | Doctoral Training Partnership
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Home page - Joint Berkeley Initiative for Microbiome Science
B6db references : phd thesis
Compared to PceA homologs that utilize cobamides with other bases, mainly benzimidazoles, and an (R)-1-aminopropan-2-ol O-2- ... multivorans and the exceptional variability of cobamides and norcobamides that can be produced by this organism. Moreover, new ... were to investigate the biosynthesis of the linker and lower base of norpseudo-B 12 and to analyze the variability of cobamides ...
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Biosynthesis4
- The enzyme is involved in the biosynthesis of phenolic cobamides in the Gram-positive bacterium Sporomusa ovata. (genome.jp)
- Deery E, Lawrence AD, Warren MJ (2022) Biosynthesis of cobamides: Methods for the detection, analysis and production of cobamides and biosynthetic intermediates. (norwichresearchpark.ac.uk)
- The aims of this study were to investigate the biosynthesis of the linker and lower base of norpseudo-B 12 and to analyze the variability of cobamides producible by S. multivorans plus their effects on the PCE-metabolism. (unipr.it)
- This study unraveled the special biosynthesis of the unique norpseudo-B 12 in S. multivorans and the exceptional variability of cobamides and norcobamides that can be produced by this organism. (unipr.it)
Metabolism1
- Some plant foods contain similar compounds called cobamides which interfere with the metabolism of true B12 and actually increase the requirement for this vitamin. (thealternativedaily.com)
Plant foods1
- But plant foods only contain B12 analogs called cobamides that block the intake of, and even increase the need for true B12, cobalamin ( 2 ). (eatsens.com)