BIOTIN SYNTHASE, A NEW MEMBER OF THE FAMILY OF ENZYMES WHICH USES S-ADENOSYLMETHIONINE AS A SOURCE OF DEOXYADENOSYL RADICAL

The fact that biotin synthase, from Escherichia coli and Bacillus spha ericus, requires S-adenosylmethionine and a reducing system led us to postulate that this synthase could belong to the family of enzymes whi ch use S-adenosylmethionine as a source of deoxyadenosyl radical, name ly pyruvate formate-lyase, lysine 2,3-aminomutase, and anaerobic ribon ucleotide reductase. We describe here experiments with S-[2,8-H-3] ade nosylmethionine and S-adenosyl-[methyl-H-3]-methionine which allowed t he identification and quantification of the expected cleavage products , deoxyadenosine, and methionine. They are formed in equimolar amounts , in a ratio close to 3 with respect to the biotin produced. We postul ate a mechanism involving the homolytic cleavage of two C-H bonds whic h should consume two equivalents of S-adenosylmethionine. The observed excess of S-adenosylmethionine consumption is attributed to abortive processes. (C) 1997 Academic Press.