Phosphoinositides. 3. Enzymic hydrolysis of inositol-containing phospholipids

Abstract

A soluble enzyme which hydrolyses phosphoinositides has been purified 50-fold from rat liver. It hydrolyzes phosphatidyl-inositol and the diphosphoinositide fraction from brain, but does not attack phosphatidylcholine, phosphatidylethanolamine, phosphatidyl-serine, phosphatidic acid or cardiolipin. For optimum activity Ca2+ ions are required. Two pH optima and other properties of the preparation are described. Two independent hydrolytic actions were found to be present in the preparation leading to the formation from phos -phatidylinositol of inositol monophosphate (phosphoinositidase C) and of glycerylphosphorylinositol (phosphoinositidases A and B.).