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Cobalamin as coenzyme: A twisting trail of research
Author(s) -
Beck William S.
Publication year - 1990
Publication title -
american journal of hematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.456
H-Index - 105
eISSN - 1096-8652
pISSN - 0361-8609
DOI - 10.1002/ajh.2830340203
Subject(s) - methylcobalamin , mutase , cobalamin , cofactor , adenosylcobalamin , chemistry , methionine synthase , enzyme , stereochemistry , biochemistry , isomerization , methionine , vitamin b12 , amino acid , catalysis
Cobalamin derivatives serve as coenzymes for the body's two cobalamin‐dependent enzymes—adenosylcobalamin‐dependent methylmalonyl CoA mutase, and methylcobalamin‐dependent methionine methyltransferase. This essay reviews, in brief form and in personal terms, the history, beginning in the mid‐1950s, of how these enzymes and coenzymes were discovered and what has been learned of their reaction mechanisms. It is clear that because of the fragility of the unique carbon‐cobalt bond in Cobalamin coenzymes, they serve primarily as free radical formers. This accounts for their efficiency in abstracting hydrogen from substrate molecules and for a subsequent chain of events that results in the isomerization of methylmalonyl CoA, the transfer of methyl groups, and (in certain bacteria) the reduction of ribonucleotides. Some thoughts are offered on the possible evolutionary significance of these facts.