Thijssen H H, Janssen Y P, Vervoort L T
Department of Pharmacology, University of Limburg, Maastricht, The Netherlands.
Biochem J. 1994 Jan 15;297 ( Pt 2)(Pt 2):277-80. doi: 10.1042/bj2970277.
This study was undertaken to search for the endogenous dithiol cofactor of the reductases of the vitamin K cycle. As a starting point, the redox-active lipophilic endogenous compounds lipoic acid and lipoamide were looked at. The study shows that microsomes contain NADH-dependent lipoamide reductase activity. Reduced lipoamide stimulates microsomal vitamin K epoxide reduction with kinetics comparable with those for the synthetic dithiol dithiothreitol (DTT). Reduced lipoic acid shows higher (4-fold) Km values. No reductase activity with lipoic acid was found to be present in microsomes or cytosol. The reduced-lipoamide-stimulated vitamin K epoxide reductase is as sensitive to warfarin and salicylate inhibition as is the DTT-stimulated one. Both vitamin K epoxide reductase and lipoamide reductase activity are recovered in the rough microsomes. NADH/lipoamide-stimulated vitamin K epoxide reduction is uncoupled by traces of Triton X-100, suggesting that microsomal lipoamide reductase and vitamin K epoxide reductase are associated. The results suggest that the vitamin K cycle obtains reducing equivalents from NADH through microsomal lipoamide reductase.
本研究旨在寻找维生素K循环中还原酶的内源性二硫醇辅因子。作为起点，研究了具有氧化还原活性的亲脂性内源性化合物硫辛酸和硫辛酰胺。研究表明，微粒体含有依赖NADH的硫辛酰胺还原酶活性。还原型硫辛酰胺刺激微粒体维生素K环氧化物还原，其动力学与合成二硫醇二硫苏糖醇（DTT）相当。还原型硫辛酸的Km值更高（4倍）。在微粒体或胞质溶胶中未发现硫辛酸具有还原酶活性。还原型硫辛酰胺刺激的维生素K环氧化物还原酶与DTT刺激的维生素K环氧化物还原酶一样，对华法林和水杨酸盐抑制敏感。维生素K环氧化物还原酶和硫辛酰胺还原酶活性均可在粗面微粒体中恢复。痕量的 Triton X-100可使NADH/硫辛酰胺刺激的维生素K环氧化物还原解偶联，这表明微粒体硫辛酰胺还原酶与维生素K环氧化物还原酶相关。结果表明，维生素K循环通过微粒体硫辛酰胺还原酶从NADH获得还原当量。
