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We previously reported (Ryu, S. H., Cho, K. S., Lee, K. Y., Suh, P. G., and Rhee, S. G. (1986) Biochem. Biophys. Res. Commun. 141, 137-144) that cytosolic fractions of bovine brain contain two phosphoinositide-specific phospholipase C (PLC), PLC-I and PLC-II. In this paper purification procedures and properties of these two forms of enzyme are presented. The two enzymes exhibit similar substrate specificity. Both PLC-I and PLC-II catalyze the hydrolysis of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2). Yet, they respond differently to activators such as Ca2+ and nucleotides and to inhibitory divalent metal ions such as Hg2+ and Cd2+. In addition, they are immunologically distinct as evidenced by the fact that monoclonal antibodies directed against either enzyme do not cross-react with the other. Their activities are Ca2+ concentration-dependent …