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Review | Special issue | Vol 28, No. 2, 1989, pp.1193-1203
Published online, 1st January, 1970
DOI: 10.3987/REV-88-SR7
Applications of Nmr Molecular Biology in Studies of the Enzyme Mechanisms of Vitamine B12 Biosynthesis

A. Ian Scott*

*Center for Biological NMR, Department of Chemistry, Texas A & M University, College Station, Texas 77843-3255, U.S.A.

Abstract

The active site of porphobilinogen (PBG) deaminase has been enriched with carbon-13 using cells of genetically engineered E. coli. Nmr spectroscopy has uncovered the structure of a novel dipyrromethane cofactor, covalently bound through Cys-242, which acts as a nucleophilic site for the covalent binding of substrate. Based on the results of pulse experiments with 13C-enriched S-adenosylmethionine (SAM), the sequence of methylation in the overall conversion of uro’gen III to cobyrinic acid is C2 > C7 > C20 > C17 > C12α > C1 > C5 > C15. These results are incorporated into a mechanistic scheme for corrin biosynthesis which also takes into account the discovery of a new series of corphinoids based on the type-I porphyrin template.