Action of organic solvents on protein kinase C

Abstract

The action of organic solvents on the biochemical and biophysical properties of protein kinase C (PKC) was measured in a defined lipid vesicle system. Chloroform, benzyl alcohol and ethanol all partially activated PKC. They had no effect on the Ca 2+- or anionic phospholipid-, phosphatidylserine-dependence. Their ability to activate PKC correlated with their lipid perturbing effect as measured by the decrease in fluorescence anisotropy. Chloroform was the most potent activator stimulating PKC phosphotransferase activity up to a level 40% of that obtained by the endogenous activator, diacylglycerol. The three fluidizers induced a more hydrophobic environment for at least one PKC tryptophan residue. This may have been due to insertion of an additional or different region of protein kinase C into the lipid bilayer as demonstrated by a blue shift in tryptophan fluorescence, providing an explanation for their inability to act as competitors of PKC binding of phorbol esters. Higher concentrations of the organic solvents resulted in a lipid bilayer that was too fluid to support membrane activity. This study demonstrates that these anesthetics and alcohols modulate lipid structure which subsequently induces PKC to undergo a different protein-lipid interaction in comparison to the endogenous activator, diacylglycerol. This supports the proposal that the biophysical state of the membrane plays a significant role in modulating PKC activity.