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 sphaericus, requires S-adenosylmethionine and a reducing system led us to postulate that this synthase could belong to the family of enzymes which use S-adenosylmethionine as a source of deoxyadenosyl radical, namely pyruvate formate-lyase, lysine 2,3-aminomutase, and anaerobic ribonucleotide reductase. We describe here experiments with S-[2,8-H-3] adenosylmethionine and S-adenosyl-[methyl-H-3]-methionine which allowed the 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 postulate a mechanism involving the homolytic cleavage of two C-H bonds which should consume two equivalents of S-adenosylmethionine. The observed excess of S-adenosylmethionine consumption is attributed to abortive processes. (C) 1997 Academic Press.