PORCINE AORTIC ENDOTHELIAL-CELL MEMBRANES CONTAIN A LPAF-COA-INDEPENDENT TRANSACYLASE

Membranes isolated from porcine aortic endothelial cells (PAEC) contain a CoA-independent transacylase enzyme (CoA-IT). CoA-IT, an integral membrane protein, transfers an acyl moiety to added [H-3]alkylhydroxyglycerophosphocholine (LPAF) to generate [H-3]alkylacylglycerophosphocholine (alkylacyl-GPC). This enzyme exhibits an apparent K(m) of 0.7 muM and a V(max) of 0.8 nmol/min per mg for the transfer of an acyl group to added [H-3]LPAF. The addition of the nonionic detergent Triton X-100 (TX-100) (0.5 mg/ml), the sulfhydryl reagents N-ethylmaleimide (NEM) (200 muM) or thimerosal (200 muM), or pre-incubating the membranes at 95-degrees-C for 10 min all decreased LPAF:CoA-IT activity by more than 95%. The inhibitory action of NEM or thimerosal suggests that sulfhydryl group(s) are involved in or are close to the catalytic site of LPAF:CoA-IT.