GTP-GAMMA-S-STIMULATED HYDROLYSIS OF PHOSPHATIDYINOSITOL-4,5-BISPHOSPHATE BY SOLUBLE PHOSPHOLIPASE-C FROM HUMAN-PLATELETS REQUIRES SOLUBLE GTP-BINDING PROTEIN

GTP-binding activity was fractionated into two peaks (GI and GII) by chromatography on heparin-agarose. GTP-dependent PLC activity eluted as a single peak, which co-chromatographed with GTP-binding peak GII. Rechromatography of peak GII on heparin-agarose, in the presence of 0.5% sodium cholate, resulted in separation of PLC and GTP-binding activities, and loss of GTP-dependent PLC activity. Recombining fractions containing PLC and GTP-binding activities restored GTP-dependent PLC activity. A specific GTP-binding protein of 29,000 daltons was identified in peak GII by Western blotting of column fractions with [.alpha.-32P]GTP. These results demonstrate that the soluble phospholipase C from human platelets is regulated by GTP S-binding protein (G29).