Fat metabolism in higher plants. Characterization of plant acyl-ACP and acyl-CoA hydrolases.

Avocado mesocarp extracts contain both acyl-CoA and acyl-acyl carrier protein (ACP) hydrolase activities. These activities have been separated by a sequence of ammonium sulfate fractionations, DEAE-cellulose, and hydroxyapatite column chromatography. Two distinct acyl-CoA hydrolase fractions and one acyl-ACP hydrolase fraction were obtained. The acyl-ACP hydrolase fraction was essentially free of acyl-CoA hydrolase activity, had a pH optimum of 9.5 and a molecular weight of 70–80,000 based on sucrose density gradient centrifugation and gel filtration chromatography. Substrate specificity studies showed that lauroyl-ACP, myristoyl-ACP, palmitoyl-ACP, and stearoyl-ACP were slowly hydrolyzed but oleoyl-ACP was rapidly hydrolyzed to free fatty acid. These results suggest a possible role for acyl-ACP hydrolase as one component of a switching system which allows, indirectly, acyl transfer from ACP to CoA derivatives in plant cells.