Lee J J, Fasco M J
Biochemistry. 1984 May 8;23(10):2246-52. doi: 10.1021/bi00305a024.
The effects of thiols and sulfhydryl blocking reagents on the reduction of vitamin K to vitamin K hydroquinone and vitamin K 2,3-epoxide to vitamin K and vitamin K hydroquinone catalyzed by rat hepatic microsomes were investigated to determine the mechanism(s) for these reactions. Both vitamin K and vitamin K 2,3-epoxide reductions were catalyzed more effectively with dithiols than with monothiols as the reductant. The sulfhydryl reagent N-ethylmaleimide (NEM) inhibited vitamin K and vitamin K 2,3-epoxide reduction much more effectively when microsomes were initially treated with dithiothreitol (prereduced). In prereduced microsomes iodoacetamide was approximately half as effective an inhibitor of vitamin K and vitamin K 2,3-epoxide reduction as NEM, but in microsomes not prereduced it was more effective. Iodoacetic acid was ineffective as an inhibitor. Vitamin K or vitamin K 2,3-epoxide added to prereduced microsomes blocked subsequent inhibition by NEM of vitamin K and vitamin K 2,3-epoxide metabolism, respectively. Vitamin K added to prereduced microsomes also blocked inhibition by NEM of vitamin K 2,3-epoxide metabolism, and vitamin K 2,3-epoxide addition blocked inhibition by NEM of vitamin K metabolism. Vitamin K did not diminish the rate of vitamin K 2,3-epoxide metabolism, however, nor did vitamin K 2,3-epoxide diminish the rate of vitamin K metabolism. These data establish that exogenous thiol compounds promote the reduction of at least one protein disulfide which participates in the metabolism of vitamin K and vitamin K 2,3-epoxide. Presumably, the resultant sulfhydryl groups are reoxidized to the disulfide form during the metabolism of either vitamin which protects them from reaction with NEM.
研究了硫醇和巯基封闭试剂对大鼠肝微粒体催化维生素K还原为维生素K氢醌以及维生素K 2,3-环氧化物还原为维生素K和维生素K氢醌的影响，以确定这些反应的机制。以二硫醇作为还原剂时，维生素K和维生素K 2,3-环氧化物的还原反应均比以单硫醇催化更有效。当微粒体先用二硫苏糖醇预处理（预还原）时，巯基试剂N-乙基马来酰亚胺（NEM）对维生素K和维生素K 2,3-环氧化物还原的抑制作用更有效。在预还原的微粒体中，碘乙酰胺对维生素K和维生素K 2,3-环氧化物还原的抑制效果约为NEM的一半，但在未预还原的微粒体中，其抑制效果更明显。碘乙酸作为抑制剂无效。添加到预还原微粒体中的维生素K或维生素K 2,3-环氧化物分别阻断了随后NEM对维生素K和维生素K 2,3-环氧化物代谢的抑制作用。添加到预还原微粒体中的维生素K也阻断了NEM对维生素K 2,3-环氧化物代谢的抑制作用，而添加维生素K 2,3-环氧化物则阻断了NEM对维生素K代谢的抑制作用。然而，维生素K并未降低维生素K 2,3-环氧化物的代谢速率，维生素K 2,3-环氧化物也未降低维生素K的代谢速率。这些数据表明，外源性硫醇化合物促进了至少一种参与维生素K和维生素K 2,3-环氧化物代谢的蛋白质二硫键的还原。据推测，在这两种维生素的代谢过程中，产生的巯基会重新氧化为二硫键形式，从而保护它们不与NEM反应。
