Björnstedt M, Kumar S, Holmgren A
Department of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden.
J Biol Chem. 1992 Apr 25;267(12):8030-4.
Selenium compounds like selenite (SeO3(2-) may form a covalent adduct with glutathione (GSH) in the form of selenodiglutathione (GS-Se-SG), which is assumed to be important in the metabolism of selenium. We have isolated GS-Se-SG and studied its reactions with NADPH and thioredoxin reductase from calf thymus or with thioredoxin reductase and thioredoxin from Escherichia coli. Incubation of 0.1 microM calf thymus thioredoxin reductase or 0.1 microM thioredoxin reductase and 1 microM thioredoxin from E. coli with 5, 10, or 20 microM GS-Se-SG resulted in a fast initial reaction, followed by a large and continued oxidation of NADPH. However, anaerobic incubation of 0.1 microM calf thymus thioredoxin reductase and 20 microM GS-Se-SG resulted only in oxidation of a stoichiometric amount of NADPH; admission of oxygen started continuous NADPH oxidation. Contrary to the mammalian enzyme, GS-Se-SG was not a substrate for thioredoxin reductase from E. coli. The rate of the oxygen-dependent reaction between calf thymus thioredoxin reductase and GS-Se-SG was increased 2-fold in the presence of 4 mM GSH, indicating that HSe- was the reactive intermediate. Glutathione reductase from rat liver reduced GS-Se-SG with a very slow continued oxidation of NADPH, and the presence of the enzyme did not affect the oxygen-dependent nonstoichiometric oxidation of NADPH by GS-Se-SG and thioredoxin reductase. Fluorescence spectroscopy showed GS-Se-SG to be a very efficient oxidant of reduced thioredoxin from E. coli and kinetically superior to insulin disulfides. Thioredoxin-dependent reduction of CDP to dCDP by ribonucleotide reductase was effectively inhibited by GS-Se-SG.
亚硒酸盐（SeO3(2-)）等硒化合物可能与谷胱甘肽（GSH）以硒代二谷胱甘肽（GS-Se-SG）的形式形成共价加合物，据推测这在硒的代谢中很重要。我们已分离出GS-Se-SG，并研究了它与来自小牛胸腺的NADPH和硫氧还蛋白还原酶或与来自大肠杆菌的硫氧还蛋白还原酶和硫氧还蛋白的反应。将0.1微摩尔/升的小牛胸腺硫氧还蛋白还原酶或0.1微摩尔/升的硫氧还蛋白还原酶与1微摩尔/升来自大肠杆菌的硫氧还蛋白与5、10或20微摩尔/升的GS-Se-SG一起温育，会导致快速的初始反应，随后是NADPH的大量持续氧化。然而，将0.1微摩尔/升的小牛胸腺硫氧还蛋白还原酶与20微摩尔/升的GS-Se-SG进行厌氧温育，仅导致化学计量的NADPH氧化；通入氧气后开始持续的NADPH氧化。与哺乳动物的酶不同，GS-Se-SG不是大肠杆菌硫氧还蛋白还原酶的底物。在4毫摩尔/升GSH存在下，小牛胸腺硫氧还蛋白还原酶与GS-Se-SG之间的氧依赖性反应速率增加了2倍，表明HSe-是反应性中间体。大鼠肝脏的谷胱甘肽还原酶还原GS-Se-SG时NADPH持续缓慢氧化，并且该酶的存在不影响GS-Se-SG和硫氧还蛋白还原酶对NADPH的氧依赖性非化学计量氧化。荧光光谱显示GS-Se-SG是大肠杆菌还原型硫氧还蛋白的非常有效的氧化剂，并且在动力学上优于胰岛素二硫化物。GS-Se-SG有效地抑制了核糖核苷酸还原酶将CDP还原为dCDP的硫氧还蛋白依赖性反应。
