Mechanistic and evolutionary aspects of vitamin B12 biosynthesis

Abstract

The B12 biosynthetic pathway requires approximately 20 enzymes to convert aminolevulinic acid, methionine and cobalt to the corrinoids. Recently several of the genes encoding the enzymes of B12 biosynthesis have been expressed in E. coli. The availability of these biosynthetic catalysts in large amounts has revolutionized the study of the B12 and heme pathways. Recent progress on the elucidation of the mechanism of several of these enzymes will be described. The technique of choice for these studies is high resolution NMR spectroscopy which can be used to detect intermediates in the catalytic cycle and to follow the overall reaction kinetics. Genetic engineering of the cDNA encoding for the biosynthetic enzymes has been used to study the mechanism of catalysis and to produce enzymes with altered substrate specificity in order to elucidate the mechanistic details of processes such as porphyrin assembly and C-methylation on the path to B12. © 1990 IUPAC