The development and application of a novel chromophoric substrate for investigation of the mechanism of yeast fatty acid synthase.

The acetyl transacylase activity of the fatty acid synthase from yeast has been investigated using p-nitrophenylthiol acetate. The chromophoric nature of the nitrophenylthiol moiety affords a convenient spectrophotometric assay for the transacylase function as well as a means to investigate the kinetics and the mechanism of this process. A probable kinetic scheme for enzyme catalyzed transacetylation from p-nitrophenylthiol acetate to an acyl acceptor (CoA or N-acetylcysteamine) is proposed and the kinetic constants for acetylation of enzyme and for acetyl transfer to an acceptor were determined. It was also demonstrated that p-nitrophenylthiol acetate can replace acetyl-CoA as a substrate in fatty acid synthesis.