VITAMIN K AND ANTICOAGULANT POISONING

在肝脏中，凝血系统中的四种凝血因子 (因子II、VII、IX和X)依赖于维生素K 生物合成。维生素是酶复合体所必需的辅因子， 依赖维生素K的羧基酶，它能将非活性前体转化为 将凝血转化为活性凝血因子。这是通过以下方式实现的 前体中特定谷氨酸残基的伽马羧化反应 蛋白质。为了作为羧基酶的辅助因子，维生素 钾必须以还原的形式存在，即维生素K对苯二酚。看起来，在 肝脏中维生素K的减少有两条独立的途径。 它们是：还原途径I；由 香豆素敏感酶维生素K环氧化物还原酶及其还原途径 由一类依赖于吡啶核苷酸的途径组成的途径 能够还原维生素K的脱氢酶。途径II 酶不太容易受到香豆素的抑制，并构成 急性心肌梗死患者凝血因子合成增强的重要途径 香豆素抗凝剂中毒。拟议的工作将集中在 这条临床上很重要的途径。该途径中的各个酶 将被提纯和鉴定，它们对抑制的敏感性 研究了不同的抗凝药物。此外，实验还包括 提出将测定凝血因子合成的体外回收率 当途径I被不可逆转地阻断时，高浓度的维生素K 通过抗凝血药物治疗。结果应该提供一个详细的体外实验 作为抢救系统的途径II的功能模型系统 抗凝剂中毒病例中凝血因子的合成。模型 将通过给抗凝大鼠注射维生素K进行体内测试。 第二条线集中在内源蛋白质底物上，用于 在整个广泛的过程中跟随酶的羧酸盐 纯化程序。提出了用多肽进行比较的方法 纯化的底物蛋白与凝血因子II和X的定位 将有可能确定内源底物是否是前体 因子II或X的形式或一种无关的蛋白质。

In the liver, four of the blood clotting factors in the coagulation system (factor II, VII, IX and X) are dependent on vitamin K for their biosynthesis. The vitamin is a necessary cofactor for an enzyme complex, the vitamin K-dependent carboxylase, that converts inactive precursors of the clotting to active clotting factors. This is achieved by Gamma-carboxylation of specific glutamic acid residues in the precursor proteins. In order to function as a cofactor for the carboxylase, vitamin K must be in its reduced form, vitamin K hydroquinone. It appears that in the liver there are two independent pathways for vitamin K reduction. These are: reduction pathway I; a pathway consisting of the coumarin-sensitive enzyme vitamin K-epoxide reductase and reduction pathway II; a pathway consisting of a class of pyridine nucleotide-dependent dehydrogenases that are capable of reducing vitamin K. The pathway II enzymes are less susceptible to inhibition by coumarins and constitute an important pathway for enhanced clotting factor synthesis in cases of coumarin anticoagulant poisoning. The work that is proposed will focus on this clinically important pathway. The individual enzymes in the pathway will be purified and identified and their susceptibility to inhibition by different anticoagulant drugs studied. In addition, experiments are proposed that will measure in vitro recovery of clotting factor synthesis by high concentrations of vitamin K when pathway I is irreversibly blocked by anticoagulant drugs. The results should provide a detailed in vitro model system for the functioning of pathway II as a salvage system for clotting factor synthesis in cases of anticoagulant poisoning. The model will be tested in vivo by administering vitamin K to anticoagulated rats. A second line of work concentrates on an endogenous protein substrate for the carboxylate that follows the enzyme throughout an extensive purification procedure. Methods are proposed which will compare by peptide mapping the purified substrate protein and clotting factors II and X. It will be possible to determine if the endogenous substrate is a precursor form of factor II or X or an unrelated protein.