The Catabolism of Phosphatidylinositol by an EDTA‐Insensitive Phospholipase A1and Calcium‐Dependent Phosphatidylinositol Phosphodiesterase in Rat Brain

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Abstract
A rat brain supernatant and microsomal fraction contained a phospholipase A1 enzyme which hydrolyzed phosphatidylinositol at pH 8 in the absence of Ca. Triolein and phosphatidylcholine were not attacked under the same incubation conditions. No evidence could be obtained for a phospholipase A2 in the microsomal preparation, and in the presence of Ca2+ the release of fatty acid observed was due to phosphatidylinositol phosphodiesterase followed by diacylglycerol lipase action. Brain phosphatidylinositol phosphodiesterase showed extensive activity in the alkaline range (7-8.5) and at pH 5-5.5. The activity at higher pH values required higher Ca concentrations and disappeared on purification of the soluble enzyme by (NH4)2SO4 fractionation. The ratio between inositol 1,2-(cyclic)phosphate and inositol 1-phosphate produced by phosphodiesterase action generally decreased with increasing pH.

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