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Abstract
Three kinds of phospholipase C [EC 3.1.4.3] were used to selectively hydrolyze phospholipids in rat liver microsomes, and their effects on the acyl-CoA: glycerophosphate and acyl-CoA: lysophospholipids acyltransferase systems were examined. The glycerophosphate acyltransferase [EC 2.3.1.15] system was inactivated rapidly by treatment with phospholipase C of Ps. aureofaciens or B. cereus and the loss of activity paralleled the degradation of phosphatidylcholine and phosphatidylethanolamine. The 1-acylglycerylphosphorylcholine acyltransferase [EC 2.3.1.23] system was only partially inactivated under the same conditions, whereas the 1-acylglycerophosphate acyltransferase [EC 2.3.1.51] system retained most of its activity even when more than 95% of phosphatidylcholine and phosphatidylethanolamine had been hydrolyzed. The results demonstrate the heterogeneity of acyltransferase systems with respect to their dependence on the intact membrane phospholipids. Hydrolysis of more than 80% of phosphatidylinositol by phosphoinositidase of B. cereus did not significantly affect these acyltransferase systems. The specificity for various acyl-CoA's of 1-acylglycerophosphate acyltransferase in microsomes treated with phospholipase C of Ps. aureofaciens was apparently different from that in untreated microsomes, while the specificity of 1-acylglycerylphosphorylcholine acyltransferase was unchanged. Saturation profiles of the acceptors were significantly different between the acyltransferase systems in phospholipase C-treated and untreated microsomes. These results suggest that 1-acylglycerophosphate and 1-acylglycerylphosphorylcholine acyltransferase systems do not require specific phospholipids such as phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol for their catalytic activities, but the integrity of these phospholipids is necessary for the proper functioning and stability of the enzymes.
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