Coenzyme B12 (cobalamin)-dependent enzymes.

@article{Marsh1999CoenzymeB,
  title={Coenzyme B12 (cobalamin)-dependent enzymes.},
  author={E. Marsh},
  journal={Essays in biochemistry},
  year={1999},
  volume={34},
  pages={
          139-54
        }
}
  • E. Marsh
  • Published 1999
  • Chemistry, Medicine
  • Essays in biochemistry
The B12 or cobalamin coenzymes are complex macrocycles whose reactivity is associated with a unique cobalt-carbon bond. The two biologically active forms are MeCbl and AdoCbl and their closely related cobamide forms. MeCbl participates as the intermediate carrier of activated methyl groups. During the catalytic cycle the coenzyme shuttles between MeCbl and the highly nucleophilic cob(I)alamin form. Examples of MeCbl-dependent enzymes include methionine synthase and Me-H4-MPT: coenzyme M methyl… Expand
Review Article Coenzyme-B(12)-Dependent Glutamate Mutase.
  • Marsh
  • Chemistry, Medicine
  • Bioorganic chemistry
  • 2000
TLDR
The enzyme serves as a paradigm for adenosylcobalamin-dependent catalysis and, more generally, provides insights into how enzymes generate and control reactive free radical species. Expand
Dissecting cobamide diversity through structural and functional analyses of the base-activating CobT enzyme of Salmonella enterica.
TLDR
Key residues in the CobT enzyme are uncovered that contribute to the diversity of cobamides in nature, and it is proposed that proper positioning of the substrates in the active site triggers the attack at the C1 ribose of NaMN. Expand
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  • Weiwen Zhang, K. Reynolds
  • Medicine, Biology
  • Journal of bacteriology
  • 2001
TLDR
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TLDR
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TLDR
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References

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TLDR
The only role thus far identified for coenzyme B12 in these reactions--namely, that of a free radical precursor--reflects the weakness, and facile dissociation, of the cobalt-carbon bond. Expand
How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 A resolution.
TLDR
The histidine-cobalt distance is very long, suggesting that the enzyme positions the histidine in order to weaken the metal-carbon bond of the cofactor and favour the formation of the initial radical species. Expand
Structure-based perspectives on B12-dependent enzymes.
Two X-ray structures of cobalamin (B12) bound to proteins have now been determined. These structures reveal that the B12 cofactor undergoes a major conformational change on binding to the apoenzymesExpand
Crystal structure of methyl-coenzyme M reductase: the key enzyme of biological methane formation.
TLDR
Together with a second structurally characterized enzyme state (MCRsilent) containing the heterodisulfide of coenzymes M and B, a reaction mechanism is proposed that uses a radical intermediate and a nickel organic compound. Expand
Coenzyme B12-dependent ribonucleotide reductase: evidence for the participation of five cysteine residues in ribonucleotide reduction.
TLDR
Results are consistent with the role of this cysteine as the protein radical responsible for initiating catalysis, and suggest that the complex role of the five cysteines is also very similar. Expand
How enzymes control the reactivity of adenosylcobalamin: effect on coenzyme binding and catalysis of mutations in the conserved histidine-aspartate pair of glutamate mutase.
TLDR
Overall, the properties of these mutants differ quite markedly from those observed when similar mutations were introduced into methionine synthase, indicating that the mutant enzymes coordinate cobalt less well. Expand
Mutations in the B12-binding region of methionine synthase: how the protein controls methylcobalamin reactivity.
TLDR
Results of mutation studies focusing on catalytic residues of vitamin B12-dependent methionine synthase show that mutation of histidine 759 blocks turnover, while mutations of aspartate 757 or serine 810 decrease the reactivity of the methylcobalamin cofactor, and propose that the reaction with AdoMet proceeds via a different transition state than the reactions with homocysteine and methyltetrahydrofolate. Expand
New function of vitamin B12: cobamide-dependent reduction of epoxyqueuosine to queuosine in tRNAs of Escherichia coli and Salmonella typhimurium
TLDR
OQ is formed when E. coli or Salmonella typhimurium is grown in glucose-salt medium and the results suggest that OQ is derived from ribose and that oQ is finally reduced to Q by a cobamide-dependent enzyme. Expand
The corrinoid-containing 23-kDa subunit MtrA of the energy-conserving N5-methyltetrahydromethanopterin:coenzyme M methyltransferase complex from Methanobacterium thermoautotrophicum. EPR spectroscopic evidence for a histidine residue as a cobalt ligand of the cobamide.
TLDR
The structural properties of MtrA1 [des-(214-239)-MtrA], which is a deletion mutant of MTRA that lacks the last 25 C-terminal hydrophobic amino acids rendering the membrane protein soluble, are reported and the results are interpreted with respect to the mechanism of energy conservation by the M trA-H complex. Expand
Vitamin B12: Experiments Concerning the Origin of Its Molecular Structure
Following the chemical synthesis of vitamin B12, a search was begun for a potentially biomimetic “dark” variant of the photochemical A/D-secocorrin → corrin cycloisomerization, the centralExpand
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