Isolation and characterization of the calcium- and phospholipid-dependent protein kinase (protein kinase C) subtypes from bovine heart

Abstract

Protein kinase C was isolated from bovine heart by chromatography on DEAE-Sephacel, phenyl-Sepharose, poly(L-lysine) agarose, and hydroxylapatite. Estimates based upon enzyme recovery indicate 10-20 nmol/min of protein kinase C activity per gram of bovine ventricular myocardium. Hydroxylapatite column chromatography resolved the preparation into two peaks of calcium- and phospholipid-dependent protein kinase activity. By Western blot analysis, peaks 1 and 2 contained subtypes II (beta 2) and III (alpha), respectively. No cross-reactivity was observed, indicating that separation was complete. Type III, the major subtype detected, was subsequently purified to apparent homogeneity by chromatography on phosphatidylserine (PS) acrylamide. Type II activity could not be recovered following phosphatidylserine affinity chromatography. Phospho amino acid analysis showed that type III autophosphorylated at serine residues, whereas type II autophosphorylated at both serine and threonine residues. Among the various phospholipids tested for activity, PS was the most effective. Both subtypes were activated by 1-stearoyl-2-arachidonylglycerol (SAG) in the presence of phosphatidylserine and calcium. Activation of both subtypes occurred at calcium concentrations of less than 1 microM. In addition to several similarities, these two subtypes showed differences in activation and kinetic properties: type II was activated by cardiolipin, 1,2-and 1,3-dioleoylglycerol, and both cis- and trans-unsaturated fatty acids. Type III was activated to a lesser degree by cardiolipin and showed no response to 1,3-dioleoylglycerol. Type III was activated to a greater extent by 1,2-diacylglycerols and by cis-unsaturated fatty acids. In the presence of PS and SAG, type II exhibited substantial activity in the presence of 1 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) without added calcium. Activation of types II and III by unsaturated fatty acids was independent of phospholipid and showed a lower apparent calcium affinity than that observed for activation by phosphatidylserine. These results show that cardiac protein kinase C subtypes II and III were functionally distinguishable and may play unique roles in the regulation of cardiac function.