Isoelectric focusing of human platelet phospholipase C: evidence for multimolecular forms

Polyacrylamide gel isoelectric focusing was employed to characterize phospholipase C activity in the supernatant fraction after disruption of human platelets. Three bands of enzyme activity were detected on focused gels: a major band of activity (B) and two additional bands (A,C) were consistently identified. The isoelectric points of the three bands were in the range of pH 7.5-8.0. Phospholipase C activity was assayed using both phosphatidylinositol and phosphatidylinositol-4-monophosphate. The prominent B band was active against both substrates and no evidence for substrate preference towards phosphoinositides was obtained. These data suggest that isozyme forms of cystolic phospholipase C are present in human platelet supernatant and suggest the possibility of functional and structural differentiation of the various forms of the enzyme.