Zwitterionic amphiphiles that raise the bilayer to hexagonal phase transition temperature inhibit protein kinase C. The exception that proves the rule.

We synthesized the zwitterionic amphiphile cholesterylphosphorylethylpyridinium. This substance activated protein kinase C (PKC) in a micelle-based assay, but in a vesicle assay it was inhibitory. An analog of this compound, in which the pyridine ring is saturated and the nitrogen methylated, showed similar behaviour with PKC. Replacing cholesterol by an aliphatic alcohol lowered the extent of activation in the micelle assay. These results demonstrate that, with some membrane additives, the vesicle and micelle assays give opposite results. Results from the membrane-based vesicle assay for PKC are in accord with the generalization that zwitterionic amphiphiles that raise the bilayer to hexagonal phase transition temperature in model membranes are inhibitors of PKC.