Fasco M J, Principe L M, Walsh W A, Friedman P A
Biochemistry. 1983 Nov 22;22(24):5655-60. doi: 10.1021/bi00293a031.
Warfarin is a potent inhibitor of vitamin K 2,3-epoxide reduction to vitamin K in vitro and in vivo. Dithiothreitol, an in vitro reductant for the vitamin K 2,3-epoxide reductase, antagonizes inhibition of the reductase by warfarin via mechanisms that have not been determined [Zimmermann, A., & Matschiner, J. T. (1974) Biochem. Pharmacol. 23, 1033-1040]. Experiments with rat hepatic microsomes were undertaken to characterize the interactions that exist between vitamin K 2,3-epoxide, warfarin, and dithiothreitol. Increasing concentrations of dithiothreitol decreased inhibition of the reductase by warfarin. When dithiothreitol was present prior to exposure of the reductase to warfarin, there was less inhibition than when the same concentration of dithiothreitol was present after its exposure to warfarin. Moreover, maximum inhibition of the reductase by warfarin occurred at a much slower rate when dithiothreitol was present initially. Inhibition of the reductase by warfarin was greater when the substrate concentration was 100 microM vitamin K 2,3-epoxide than when it was 10 microM epoxide. On the basis of these data, we conclude that (i) dithiothreitol reduces either directly or indirectly a critical disulfide within the reductase that it reoxidized during reduction of the epoxide substrate, (ii) warfarin and vitamin K 2,3-epoxide are not competitive with respect to one another, and (iii) warfarin binding, which produces inhibition, occurs solely to the disulfide form of the reductase. Once it is bound, warfarin inhibits further reduction of the critical disulfide by dithiothreitol. Dithiothreitol therefore antagonizes warfarin by maintaining the reductase in the reduced state.
华法林在体内外均是维生素K 2,3 - 环氧化物还原为维生素K的强效抑制剂。二硫苏糖醇是维生素K 2,3 - 环氧化物还原酶的体外还原剂，它通过尚未明确的机制对抗华法林对该还原酶的抑制作用[齐默尔曼，A.，& 马施纳，J. T.（1974年）《生物化学与药理学》23卷，第1033 - 1040页]。开展了大鼠肝微粒体实验，以表征维生素K 2,3 - 环氧化物、华法林和二硫苏糖醇之间存在的相互作用。二硫苏糖醇浓度的增加降低了华法林对还原酶的抑制作用。当在还原酶接触华法林之前存在二硫苏糖醇时，抑制作用比在其接触华法林后存在相同浓度二硫苏糖醇时要小。此外，当初始存在二硫苏糖醇时，华法林对还原酶的最大抑制作用出现的速度要慢得多。当底物浓度为100微摩尔维生素K 2,3 - 环氧化物时，华法林对还原酶的抑制作用比对10微摩尔环氧化物时更大。基于这些数据，我们得出以下结论：（i）二硫苏糖醇直接或间接还原还原酶内一个关键的二硫键，该二硫键在环氧化物底物还原过程中被重新氧化；（ii）华法林和维生素K 2,3 - 环氧化物彼此之间不存在竞争关系；（iii）产生抑制作用的华法林结合仅发生在还原酶的二硫键形式上。一旦结合，华法林会抑制二硫苏糖醇对关键二硫键的进一步还原。因此，二硫苏糖醇通过使还原酶保持还原状态来对抗华法林。
