Purification and Properties of a Palmityl Thioesterase II from Escherichia coli

A palmityl thioesterase II which is insensitive to inhibition by diisopropyl fluorophosphate has been purified 20-fold from extracts of Escherichia coli. This enzyme exhibits properties which distinguish it from the more substratespecific diisopropyl fluorophosphate-sensitive palmityl thioesterase I known also to be present in E. coli. The present palmityl thioesterase II has a general specificity for long chain fatty acyl thioesters of coenzyme A or acyl carrier protein. The enzyme will catalyze the hydrolysis of saturated, unsaturated, or β-hydroxy fatty acyl coenzyme A thioesters. Palmityl, palmitoleyl, and d(-)-β-hydroxymyristyl derivatives are the preferred substrates in each respective series of homologues and Vmax values are 0.53, 0.49, and 0.20 µmole per min per mg, respectively, for each CoA thioester.