Inhibitory action of chlorpromazine, dibucaine, and other phospholipid-interacting drugs on calcium-activated, phospholipid-dependent protein kinase.

Ca2+-activated, phospholipid-dependent protein kinase recently found in mammalian tissues (Takai, Y., Kishimoto, A., Iwasa, Y., Kawahara, Y., Mori, T., and Nishizuka, Y. (1979) J. Biol. Chem. 254, 3692-3695) is inhibited by various phospholipid-interacting drugs such as chlorpromazine, imipramine, phentolamine, dibucaine, verapamil, and tetracaine. This effect is attributed to the inhibition of the activation process but not to the interaction with the active site of enzyme. This is supported by the fact that a catalytic fragment of this enzyme, which is obtained by limited proteolysis with Ca2+-dependent neutral protease, is fully active without without Ca2+ and phospholipid and is not susceptible to any of these drugs. Kinetic analysis suggests that these drugs cause such inhibition competitively with phospholipid. None of these drugs appears to compete with Ca2+ or to counteract the unique effect of unsaturated diacylglycerol. Unsaturated diacylglycerol has been shown previously to increase markedly the affinity of enzyme for Ca2+ as well as for phospholipid and thereby serve as an initiator for the activation of this protein kinase. Neither cyclic AMP-dependent nor cyclic GMP-dependent protein kinase is susceptible to these phospholipid-interacting drugs.