Cooperative roles of various membrane phospholipids in the activation of calcium-activated, phospholipid-dependent protein kinase.

Although phosphatidylserine is the sole phospholipid effective for the activation of Ca2+-activated, phospholipid-dependent protein kinase in the presence of a small amount of unsaturated diacylglycerol and micromolar concentrations of Ca2+ (Takai, Y., Kishimoto, A., Kikkawa, U., Mori, T., and Nishizuka, Y. (1979) Biochem. Biophys. Res. Commun. 91, 1218-1224), other species of phospholipids modulate the activation of enzyme considerably. When phosphatidylserine is supplemented with phosphatidylethanolamine, further enhancement of the enzymatic activity is observed. Inversely, the addition of phosphatidylcholine or sphingomyelin markedly diminishes the enzyme activation by phosphatidylserine. Phosphatidylinositol, which serves as the source of unsaturated diacylglycerol, and phosphatidic acid do not show significant effects. Kinetic analysis has indicated that phosphatidylethanolamine enhances the enzyme activation by marked increase in the affinity of enzyme for Ca2+ and also by slight increase in the affinity for phosphatidylserine as well as for unsaturated diacylglycerol without affecting the maximum reaction velocity. Phosphatidylcholine and sphingomyelin diminish the enzyme activation in an uncompetitive manner with respect to Ca2+ and in a competitive manner with respect to both phosphatidylserine and unsaturated diacylglycerol. These results suggest that each species of the various membrane phospholipids plays a specific role with positive or negative cooperativity in the activation of this unique protein kinase.