Walker F J, Chavin S I, Fay P J
Arch Biochem Biophys. 1987 Jan;252(1):322-8. doi: 10.1016/0003-9861(87)90037-3.
Factor VIII was inactivated by activated protein C in the presence of calcium and phospholipids. Analysis of the activated protein C-catalyzed cleavage products of factor VIII indicated that inactivation resulted from the cleavage of the heavy chains. The heavy chains appeared to be converted into 93- and 53-kDa peptides. Inactivation of factor VIII that was only composed of the 93-kDa heavy chain and 83-kDa light chain indicated that the 93-kDa polypeptide could be degraded into a 68-kDa peptide that could be subsequently cleaved into 48- and 23-kDa polypeptides. Thus, activated protein C catalyzed a minimum of four cleavages in the heavy chain. Activated protein C did not appear to alter the factor VIII light chain. The addition of protein S accelerated the rate of inactivation and the rate of all of the cleavages. The effect of protein S could be observed on the cleavage of the heavy chains and on secondary cleavages of the smaller products, including the 93-, 68-, and 53-kDa polypeptides. The addition of factor IX to the factor VIII-activated protein C reaction mixture resulted in the inhibition of factor VIII inactivation. The effect of factor IX was dose dependent. Factor VIII was observed to compete with factor Va for activated protein C. The concentration dependence of factor VIII inhibition of factor Va inactivation suggested that factor VIII and factor Va were equivalent substrates for activated protein C.
在钙和磷脂存在的情况下，凝血因子VIII被活化蛋白C灭活。对活化蛋白C催化的凝血因子VIII裂解产物的分析表明，灭活是由重链的裂解导致的。重链似乎被转化为93 kDa和53 kDa的肽段。仅由93 kDa重链和83 kDa轻链组成的凝血因子VIII的灭活表明，93 kDa的多肽可降解为68 kDa的肽段，随后可裂解为48 kDa和23 kDa的多肽。因此，活化蛋白C催化重链至少发生四次裂解。活化蛋白C似乎并未改变凝血因子VIII的轻链。蛋白S的添加加速了灭活速率以及所有裂解的速率。蛋白S的作用可在重链的裂解以及较小产物（包括93 kDa、68 kDa和53 kDa多肽）的二次裂解中观察到。向凝血因子VIII - 活化蛋白C反应混合物中添加凝血因子IX导致凝血因子VIII灭活受到抑制。凝血因子IX的作用呈剂量依赖性。观察到凝血因子VIII与因子Va竞争活化蛋白C。凝血因子VIII对因子Va灭活的抑制作用的浓度依赖性表明，凝血因子VIII和因子Va是活化蛋白C的等效底物。
