Properties of protein kinase C subspecies in human platelets.

Protein kinase C (PKC) from human platelets was resolved into two fractions by hydroxyapatite column chromatography. One of the enzymes was indistinguishable from the brain type III PKC having alpha-sequence in its kinetic and immunological properties. The other enzyme was kinetically different from any of the brain PKC subspecies so far isolated, although it resembled the brain type II PKC having beta-sequence. With H1 histone as substrate, this platelet enzyme was not very sensitive to Ca2+, and activated partly by phosphatidylserine plus diacylglycerol or by free arachidonic acid. Both platelet enzymes could phosphorylate the P47 protein in vitro, but the enzyme physiologically responsible for the P47 protein phosphorylation in the activated platelets remains to be identified.