Resolution and Reconstitution of the Phosphatidate-Synthesizing System of Rat-Liver Microsomes

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Abstract
The phosphatidate-synthesizing system of rat-liver microsomes was resolved into two component enzymes, glycerolphosphate acyltransferase and 1-acylglycerolphosphate acyltransferase. The resolution is effected by sucrose density gradient centrifugation in the presence of a nonionic detergent, Triton X-100. Combination of both enzymes results in reconstitution of the phosphatidate-synthesizing system. These results establish that two distinct enzymes, glycerolphosphate acyltransferase and 1-acylglycerolphosphate acyltransferase, are required for synthesis of phosphatidic acid from sn-glycerol 3-phosphate. Furthermore, the 1-acylglycerolphosphate acyltransferase preparation efficiently uses unsaturated (or saturated) fatty acyl-CoA as acyl donor. Our previous studies showed that the glycerolphosphate acyltransferase preparation catalyzes formation of 1-acylglycerol 3-phosphate, using preferentially saturated fatty acyl-CoA as acyl donor. These findings indicate that the reconstituted system is capable of yielding phosphatidic acid with an asymmetric fatty acid distribution.

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