A Physical Mode of Inhibitory Action of Phospholipid-Interacting Compounds on The Activation of Cellular Protein Kinase C

Abstract

A relationship between the inhibition of protein kinase C activation by phospholipid -interacting compounds and the associated change in the physical properties of phospholipid vesicle membranes was studied using physically characterizable phosphatidylserine -phosphatidylcholine-diacylglycerol (3:6:1) mixture vesicle membranes. The vesicles supported protein kinase C activation as well as phosphatidylserine-diacylglycerol (9:1) vesicles. Under the same enzyme assay conditions, trifluoperazine and to a lesser degree chlorpromazine inhibited the enzyme activation and increased the fluorescence polarization of 1,6-diphynylhexatriene in the vesicle membranes in a dose-related fashion. At the concentration of 10^-4M, n-dibutyltin dichloride also showed a slight tendency to inhibit the enzyme activation and to increase the polarization whereas dibucaine scarcely showed any significant effect. At least DBC of more than 5×10^-4M was required for manifestation of the detectable effect.There was a good correlation between the relative order of potency of these compounds for the inhibition of the enzyme activation and for the ordering of the membranes. Moreover, the compounds inhibited the enzyme and substrate binding to the vesicle membranes in a dose-related fashion. These results shows that the phospholipids -interacting compounds such as trifluoperazine and chlorpromazine may exert their inhibitory action on the enzyme activation by ordering the vesicle membranes or by the change in phase separation.