Activation of protein kinase C by Triton X-100 mixed micelles containing diacylglycerol and phosphatidylserine.

A mixed micellar assay for protein kinase C was developed to investigate the specificity and stoichiometry of activation by phospholipids and diacylglycerols. Triton X-100 mixed micelles containing 8 mol % phosphatidylserine (PS) and 2.5 mol % sn-1,2-dioleoylglycerol (diC18:1) activated rat brain protein kinase C in the presence of Ca2+ to the same degree as sonicated PS/diC18:1 did in the standard assay. However, protein kinase C activity was more responsive to diC18:1 in the mixed micellar assay than the standard assay. At 8 mol % PS and 100 microM Ca2+, diC18:1 stimulated maximally at 1 mol %. At 2.5 mol % diC18:1 and 100 microM Ca2+, PS did not activate until 3 mol % and then did so cooperatively with maximal stimulation occurring at 6-8 mol %. Direct evidence for a Ca2+-, PS-, and diC18:1-dependent interaction of protein kinase C with mixed micelles was obtained by molecular sieve chromatography on Sephacryl S-200. These data permit inferences pertaining to the number of diC18:1 and PS molecules/micelle which are required for activation. For diC18:1, a single molecule may be sufficient but no more than 2 molecules are required. For PS, greater than 4 but less than 10 molecules are required. These data establish that a phospholipid bilayer is not required for protein kinase C activation and that activation of monomeric protein kinase C occurs.