Salem H H, Broze G J, Miletich J P, Majerus P W
J Biol Chem. 1983 Jul 25;258(14):8531-4.
Protein C, a vitamin K-dependent protein, circulates in plasma as an inactive precursor. Once activated, it possesses potent anticoagulant activity through the inactivation of factors Va and VIIIa. Thrombin, the only known physiologic activator of this protein, is catalytically inefficient. Thrombomodulin, a protein purified from rabbit lungs, has been reported to enhance protein C activation by thrombin. We have previously demonstrated that factor Va, a substrate for activated protein C, is also a thrombin cofactor in the activation of protein C (Salem, H.H., Broze, G.J., Miletich, J. P., and Majerus, P.W. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 1584-1588). When factor Va is fractionated to its individual components, only the light chain (Mr 78,000) has thrombin cofactor activity. Although factor Va and thrombomodulin can both stimulate thrombin-catalyzed protein C activation, the physiological relationship between these two proteins remains to be determined.
蛋白C是一种维生素K依赖蛋白，以无活性前体形式存在于血浆中。一旦被激活，它通过灭活因子Va和VIIIa而具有强大的抗凝活性。凝血酶是已知的该蛋白唯一的生理性激活剂，其催化效率较低。从兔肺中纯化得到的血栓调节蛋白据报道可增强凝血酶对蛋白C的激活作用。我们之前已经证明，活化蛋白C的底物因子Va也是蛋白C激活过程中的凝血酶辅因子（塞勒姆，H.H.，布罗兹，G.J.，米莱蒂奇，J.P.，和马耶鲁斯，P.W.（1983年）《美国国家科学院院刊》80，1584 - 1588）。当将因子Va分离成其各个组分时，只有轻链（分子量78,000）具有凝血酶辅因子活性。尽管因子Va和血栓调节蛋白都能刺激凝血酶催化的蛋白C激活，但这两种蛋白之间的生理关系仍有待确定。
