Differences between microsomal and mitochondrial-matrix palmitoyl-coenzyme A hydrolase, and palmitoyl-l-carnitine hydrolase from rat liver

Abstract

Palmitoyl-CoA hydrolase (EC 3.1.2.2) and palmitoyl-L- carnitine hydrolase (EC 3.1.1.28) activities from rat liver were investigated. Microsomal and mitochondrial-matrix palmitoyl-CoA hydrolase activities had similar pH and temperature optima, but the activities showed different temperature stabilities; they were inhibited by Pb2+ and Zn2+. The palmitoyl-CoA hydrolase activities in microsomal fraction and mitochondrial matrix were differently affected by the addition of Mg2+, Ca2+, Co2+, K+ and Na+ to the reaction mixture. ATP, ADP and NAD+ stimulated the microsomal activity and inhibited the mitochondrial-matrix enzyme. The activity of both the microsomal and mitochondrial-matrix hydrolase enzymes was specific for long-chain fatty acyl-CoA esters (C12-C18), with the highest activity for palmitoyl-CoA. The apparent Km for palmitoyl-CoA was 47 .mu.M for the microsomal enzyme and 17 .mu.M for the mitochondrial-matrix enzyme. The palmitoyl-CoA hydrolase and palmitoyl-L-carnitine hydrolase activities of microsomal fraction had similar pH optima and were stimulated by dithiothreitol but were affected differently by the addition of Pb2+, Mg2+, Ca2+, Mn2+ and cysteine. The 2 enzymes had different temperature-sensitivities. Palmitoyl-CoA hydrolase and palmitoyl-L-carnitine hydrolase are apparently separate microsomal enzymes and the hydrolysis of palmitoyl-CoA in the microsomal fraction and mitochondrial matrix is catalyzed by 2 different enzymes.