Biotin synthase mechanism: on the origin of sulphur

Biotin synthase catalyses the last step of the biosynthesis of biotin in mi croorganisms and plants. The active protein isolated from Bacillus sphaeric us and Escherichia coli contains an iron-sulphur (FeS) cluster. The native enzymes mere depleted of their iron and inorganic sulphide and the resultin g apoenzymes mere chemically reconstituted with FeCl3 and Na-2[S-34] to giv e labelled ((FeS)-S-34) enzymes. These enzymes were functional and when ass ayed in vitro produced labelled biotin containing about 65% of S-34. These data strongly support the hypothesis that the sulphur of biotin is derived from the (FeS) centre of the enzyme. (C) 1998 Federation of European Bioche mical Societies.