The presence of Ca(2+)-independent phospholipase A1 highly specific for phosphatidylinositol in bovine brain

EDTA-insensitive phospholipase A activity hydrolyzing phosphatidylinositol was detected in a bovine brain soluble fraction. This phospholipase A was purified 25-fold by sequential chromatographies of DEAE-Toyopearl, Phenyl-Toyopearl, and Ultrahydrogel 1000. The partially purified EDTA-insensitive phospholipase A showed an apparent molecular mass of 230kDa on an Ultrahydrogel 1000 column in the presence of 0.05% Triton X-100 and a pH optimum at 7.0. The enzyme was highly specific for phosphatidylinositol, phosphatidylethanolamine and phosphatidylcholine were not hydrolyzed significantly. The enzyme activity was characterized as phospholipase A 1 , and Ca 2+ and Mg 2+ were not required for its activity. These results indicate the existence of Ca 2+ -independent, phosphatidylinositol-specific metabolism besides those catalyzed by Ca 2+ -dependent phospholipase A 2 and Ca 2+ -dependent, phosphatidylinositol-specific phospholipase C.