Enoyl coenzyme A reduction by bovine mammary fatty acid synthetase. Specificity and other characteristics.

The NADPH-dependent enoyl coenzyme A reductase activity of bovine mammary fatty acid synthetase has been characterized with regard to substrate specificity and the product formed. A relatively high specificity for an unsubstituted, four-carbon, 2,3-enoyl chain in trans configuration is obtained. Reduction of trans-crotonyl-CoA results in butyrate, 50% of which is coenzyme A-bound. The reaction is subject to product inhibition, specifically by butyryl-CoA and NADP. Free coenzyme A, on the other hand, is an activator. The pH profile, susceptibility to inhibition by -SH reagents, the results of the relative activities obtained with substrate analogues and homologues, and the ready use of crotonyl-CoA as a primer in fatty acid synthesis are consistent with a mechanism in which the crotonyl group is transferred to an -SH group, is reduced, and then is either transferred back to CoA or hydrolyzed.