Hybridization studies of chicken liver fatty acid synthetase. Evidence for the participation in palmitate synthesis of cysteine and phosphopantetheine sulfhydryl groups on adjacent subunits.

Abstract

Enzymatically inactive variants of chicken liver fatty acid synthetase have been prepared by specific chemical modification of the active cysteine SH group with iodoacetamide, and the phosphopantetheine SH group with chloroacetyl-CoA. Hybridization of each of these variants with the unmodified enzyme yielded (modified)-(unmodified) hybrid dimers which possessed 50% synthetase activity. A 50% active (iodoacetamide-modified)-(chloroacetyl-CoA-modified) hybrid dimer was also demonstrated by recombination of these variants with each other. These results indicate that the two functional sites on the synthetase are independently active, and that each is comprised of a cysteine SH group from one subunit and a complementary phosphopantetheine SH group from the other subunit as depicted by the head-to-tail arrangement proposed by Wakil and co-workers (Wakil, S. J., Stoops, J. K., and Joshi, V.C.