[A study on the participation of protein kinase C in the blood coagulation].

Although the cascade theory is the main story which explains mechanisms of blood coagulation, the interactions among the enzymes (i. e. coagulation factors) involved in this cascade has not been well characterized. In this paper, protein kinase C (phospholipid/Ca(2+)-dependent protein kinase) was found to involve in the phosphorylation of the coagulation factors (I, II and VIII), which require both phospholipid and Ca2+ for their activations. In the phosphorylation of prothrombin (blood coagulation factor II), the apparent Km value of 0.86 microM was obtained. The value was comparable to that reported for most known substrates of protein kinase C. A 2-dimensional separation-analysis revealed that serine residue was apparently phosphorylated by PKC. The phosphorylation was inhibited by protein kinase C inhibitors such as gossypol and staurosporine. Prothrombin seemed to have a tendency to be increased in its coagulation activity (1. e. shortening of prothrombin time), when it was phosphorylated by PKC. These phenomena suggest that PKC may be involved in the mechanism of blood coagulation.