The Enzymatic Acylation of Lysophosphatidylinositol.

Lysophosphatidylcholine (1)) lysophosphatidylethanolamine (2), and lysophosphatidic acid (3) have been shown to react with fatty acid thioesters of coenzyme A to form the diacyl phosphatides. Preliminary work from this laboratory (4) demonstrated the presence of lysophosphatidylinositol in pigeon pancreas and the acylation of this lysophosphatide in the presence of oleic acid, coenzyme A, and adenosine triphosphate. The present paper is a more detailed study of the acylation of 3*P-labeled lysophosphatidylinositol. The lysophosphatidylinositol substrate was prepared by the enzymatic deacylation of radioactive phosphatidylinositol from pigeon pancreas. A very simple and precise assay method was developed which permits the acylation reaction to be followed. With this method, it has been possible to study the conditions under which the acyl group is transferred from acyl-CoA to lysophosphatidylinositol. Comparisons were also made between the rate of transfer of a saturated (palmityl-) and an unsaturated (oleyl-) CoA derivative. The relative rates of acylation of lysophosphatidylcholine and lysophosphatidylinositol were also compared, and preliminary kinetic studies were undertaken in an attempt to elucidate the mechanism of this reaction.