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Review | Regular issue | Vol 2, No. 1, 1974, pp.125-152
Published online, 1st January, 1970
DOI: 10.3987/R-1974-01-0125
Concerting the Biosynthesis of Vitamin B12

A. Ian Scott*

*Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, CT 06511, U.S.A.

Abstract

The use of 13C FT-NMR has led to the observation that while 8 molecules of [2-13C] -ALA are incorporated into vitamin B12 in P. shermanii, [5-13C]-ALA labels only seven of the carbon atoms of cyanocobalamin i.e. one of the amino methyl groups of ALA is “lost” in the process. It has also been confirmed that seven of the methyl groups of B12 are derived from 13CH3 enriched methionine and further that the chirality of the gem-dimethyl grouping at C12 labeled with [13CH3]-methionine is R. A soluble enzyme mixture from the 37,000 g supernatant of disrupted cells of P. shermanii converts both 14C-labeled ALA and 14C-uro’gen III to cobyrinic acid, the simplest corrinoid material on the pathway to vitamin B12 and the coenzyme in presence of NADPH, Co++ , Mg++, S-adenosylmethionine and glutathione. A detailed hypothesis of the mechanism of corrin synthesis from uro’gen III has been developed.