Tans G, Rosing J, Griffin J H
J Biol Chem. 1983 Jul 10;258(13):8215-22.
When purified human blood coagulation Factor XII (Hageman factor) is incubated with sulfatides at 37 degrees C, activation of Factor XII occurs as judged by the appearance of amidolytic activity towards the chromogenic substrate H-D-Pro-Phe-Arg-p-nitroanilide. Polyacrylamide gel electrophoresis studies using 125I-Factor XII as a marker show that the appearance of amidolytic activity correlates with Factor XII cleavage, that activation goes to completion and that virtually all Factor XIIa formed is present as the two-chain, 80,000 Mr form, alpha-Factor XIIa. Rigorous analysis of kinetic data establishes that, between 0.02 and greater than 90% of the reaction, the activation of Factor XII is described by a mechanism of autoactivation of Factor XII by Factor XIIa. The rate of autoactivation increases with increasing Factor XII concentrations at constant sulfatide levels but decreases with increasing sulfatide concentrations at constant levels of Factor XII. These findings suggest that the concentrations of Factor XII and Factor XIIa bound to the sulfatide surface determine the rate of autoactivation. Soybean trypsin inhibitor, Trasylol, and anti-prekallikrein antibodies have no influence on the rate of sulfatide-dependent autoactivation of Factor XII. Benzamidine inhibits autoactivation with an inhibitor constant, Ki, of 1.9 mM which is similar to the Ki of 1.5 mM for the enzyme, alpha-Factor XIIa. Thus, sulfatide-dependent activation of purified Factor XII is not due to contaminating proteases and is described by a second order mechanism of autoactivation due to the action of surface-bound Factor XIIa on surface-bound Factor XII.
当纯化的人凝血因子 XII（哈格曼因子）与硫脂在 37℃孵育时，根据对生色底物 H-D-脯氨酸-苯丙氨酸-精氨酸-对硝基苯胺的酰胺水解活性的出现判断，因子 XII 发生激活。使用 125I-因子 XII 作为标记的聚丙烯酰胺凝胶电泳研究表明，酰胺水解活性的出现与因子 XII 的裂解相关，激活反应可进行到底，并且几乎所有形成的因子 XIIa 都以 80,000 分子量的双链形式，即α-因子 XIIa 存在。对动力学数据的严格分析表明，在 0.02 至超过 90%的反应过程中，因子 XII 的激活由因子 XIIa 对因子 XII 的自动激活机制描述。在硫脂水平恒定的情况下，自动激活速率随因子 XII 浓度的增加而增加，但在因子 XII 水平恒定的情况下，随硫脂浓度的增加而降低。这些发现表明，结合在硫脂表面的因子 XII 和因子 XIIa 的浓度决定了自动激活的速率。大豆胰蛋白酶抑制剂、抑肽酶和抗前激肽释放酶抗体对因子 XII 的硫脂依赖性自动激活速率没有影响。苯甲脒以 1.9 mM 的抑制常数 Ki 抑制自动激活，这与酶α-因子 XIIa 的 1.5 mM 的 Ki 相似。因此，纯化的因子 XII 的硫脂依赖性激活不是由于污染的蛋白酶引起的，而是由表面结合的因子 XIIa 对表面结合的因子 XII 的作用所导致的二级自动激活机制所描述。
