Studies on the mechanism of fatty acid synthesis. XVI. Preparation and general properties of acyl-malonyl acyl carrier protein-condensing enzyme from Escherichia coli.

Acyl-malonyl acyl carrier protein (ACP)-condensing enzyme, prepared from extracts of Escherichia coli, catalyzes the condensation of acetyl-ACP and malonyl-ACP to form acetoacetyl-ACP. It also catalyzes the condensation of various longer chain saturated acyl-ACP derivatives with malonyl-ACP to form the P-ketoacyl-ACP of the longer homologues. The enzyme is specific for the acyl-ACP derivatives and does not act on acyl coenzyme A derivatives (acetyl-CoA or malonyl-CoA). The enzyme has a functional -SH group and can be readily inhibited by -SH-binding reagents such as N-ethylmaleimide and iodoacetamide. Acetyl-ACP protects the enzyme against thiol-binding reagents, which indicates that an acetyl-S-enzyme complex may be an intermediate in the condensation of acyl-ACP and malonyl-ACP to form fi-ketoacyl-ACP.