A protein kinase system from platelet rich plasma.

Treatment of platelet rich plasma (PRP) at pH 5 results in the precipitation of a protein kinase system. The protein kinase is associated with the platelet fraction and is capable of phosphorylation of several plasma proteins. Analysis of the 32P-labeled phosphoproteins by two dimensional gel electrophoresis showed the existence of three major phosphoproteins: 72K and 80K proteins with identical isoelectric points (pI) of 6.0 and another 72K protein with a pI of 6.8-7.0. This latter 72K phosphoprotein has recently been identified as the alpha-chain of fibrinogen. The identity of the other 2 proteins remains to be shown. The activity of the protein kinase is markedly enhanced by Mn2+, it phosphorylates calf thymus histone as an exogenous substrate and is independent of cAMP or cGMP. This protein kinase activity is inhibited competitively by ADP.