Silverman R B, Nandi D L
Department of Chemistry, Northwestern University, Evanston, Illinois 60208.
Biochem Biophys Res Commun. 1988 Sep 30;155(3):1248-54. doi: 10.1016/s0006-291x(88)81274-9.
Vitamin K 2,3-epoxide reductase activity from liver microsomes requires only a thiol cofactor, particularly dithiothreitol (DTT). In order to identify a likely physiological cofactor, reduced lipoic acid and reduced thioredoxin were tested as cofactors in beef and rat liver microsomal systems. Reduced lipoic acid is only about one-third as active as DTT in both systems. Thioredoxin, however, is significantly more active than either DTT or reduced lipoic acid in both systems; thioredoxin binds 188 times better than does DTT. The thioredoxin must be in the reduced form since omission of either thioredoxin reductase or NADPH results in complete loss of enzyme activity. The concentration of DTT required to obtain maximal enzyme activity may be as much as 485 times greater than the corresponding concentration of reduced thioredoxin that gives the same enzyme activity.
来自肝脏微粒体的维生素K 2,3 - 环氧化物还原酶活性仅需要一种硫醇辅因子，特别是二硫苏糖醇（DTT）。为了确定一种可能的生理辅因子，在牛肉和大鼠肝脏微粒体系统中测试了还原型硫辛酸和还原型硫氧还蛋白作为辅因子的情况。在这两个系统中，还原型硫辛酸的活性仅约为DTT的三分之一。然而，在这两个系统中，硫氧还蛋白的活性明显高于DTT或还原型硫辛酸；硫氧还蛋白的结合能力比DTT强188倍。硫氧还蛋白必须处于还原形式，因为省略硫氧还蛋白还原酶或NADPH会导致酶活性完全丧失。获得最大酶活性所需的DTT浓度可能比产生相同酶活性的还原型硫氧还蛋白的相应浓度高多达485倍。
