PURIFICATION, CHARACTERIZATION AND MODULATION OF A MICROSOMAL CARBOXYLESTERASE IN RAT-LIVER FOR THE HYDROLYSIS OF ACYL-COA

A carboxylesterase containing long-chain acyl-CoA hydrolase activity w as purified to apparent homogeneity from rat liver microsomes. Palmito yl-CoA was the most preferred substrate, followed by stearoyl-CoA and oleoyl-CoA. Arachidonoyl-CoA, linoleoyl-CoA and acetyl-CoA were not hy drolysed by the enzyme. The purified enzyme had no activity on the hyd rolysis of phospholipids and neutral lipids. The molecular mass of the enzyme was found to be 56 kDa by SDS/PAGE and 64 kDa by gel-filtratio n chromatography. On isoelectric focusing, the purified enzyme behaved like the ES-4 type, with a pI of 6.15. Determination of the amino aci d sequence revealed that its N-terminal sequence is 100% homologous wi th the only other known N-terminal sequence for a rat carboxylesterase isoenzyme (ES-10). Enzyme activity was inhibited by lysophosphatidic acid and activated by lysophosphatidylcholine. The modulation of enzym e activity by these lysophospholipids might represent a plausible mech anism for the physiological control of acyl-CoA concentrations.