EVIDENCE FOR THE PROBABLE FINAL STEPS IN AFLATOXIN BIOSYNTHESIS

The final steps in the biosynthesis of the potent environmental carcinogen aflatoxin B-1 (8) are believed to involve the oxidative cleavage and rearrangement of O-methylsterigmatocystin (7) with loss of a C-1-unit. The means by which this overall transformation occurs is not known and has been addressed using cell-free conversions of samples of radiolabeled 7 that were obtained by the incorporation of either [1-C-14]- or [2-C-14]acetate. The proportion of radioisotope detected in aflatoxin B-1 relative to that of the C-1-unit liberated (formaldehyde, formic acid, or carbon dioxide) was tested. [C-14]Carbon dioxide alone was isolated in the proper stoichiometry to limit the possible mechanisms that can be acting at the conclusion of this biosynthetic pathway.