Bioconversion of dethiobiotin to biotin by a cell-free system of a bioYB transformant of Bacillus sphaericus

The bioconversion of dethiobiotin to biotin has been demonstrated by cell-free extracts of a biotin-hyperproducing Bacillus sphaericus mutant transformed with an expression vector for two bio genes: bioB, encoding biotin synthase; and bioY, the function of which remains unknown. The reaction mixture for the biosynthesis of biotin contained yeast extract, l-cysteine and sucrose as well as dethiobiotin. The cell-free extracts prepared from protoplasts of the transformant with a French press at not more than 1000 kg cm−2 showed appreciable biotin synthase activities. An unusually high protein concentration (more than 18 mg ml−1) in the reaction mixture was required for the enzyme activity, while cell-free extracts of less than 10 mg protein ml−1 hardly exhibited detectable activities. The product from dethiobiotin in a reaction mixture was identified as biotin by bioautography with Lactobacillus plantarum.