Protein kinase C penetration into lipid bilayers

Physical characteristics of the association and subsequent penetration of protein kinase C into defined lipid bilayers were analyzed using four different fluorescence probes. The enzyme demonstrated strong hydrophobic and electrostatic interactions with the bilayer as suggested by its ability to increase permeability of carboxyfluorescein-filled unilamellar vesicles. The intensity of interaction was dependent on the concentration of phosphatidylserine. The hydrophilic quencher, N-methylpicolinium perchlorate, was used to show that the tryptophan residues affected by ligand-induced conformational changes were in a hydrophobic region(s) of the enzyme. Using quenching of intrinsic tryptophan fluorescence, the enzyme was shown to penetrate the lipid bilayer to the C-16 position of labeled fatty acid probes. The association and subsequent penetration of the enzyme into the lipid bilayer was independent of divalent cations in these systems and had no significant effect on activator-independent substrate phosphorylation.