DeMaster E G, Quast B J, Redfern B, Nagasawa H T
Medical Research Laboratories, Department of Veterans Affairs Medical Center, Minneapolis, Minnesota 55417, USA.
Biochemistry. 1995 Sep 12;34(36):11494-9. doi: 10.1021/bi00036a023.
Nitric oxide (NO) generated by diethylamine nonoate (DEA/NO), an NO donor, readily oxidized the free sulfhydryl group of human serum albumin (HSA) as well as the sulfhydryl groups of reduced glutathione (GSH) and dithiothreitol (DTT) at pH 7.4 and 37 degrees C. Under anaerobic conditions, the major products of the oxidation of HSA thiol by NO were the sulfenic acid (RSOH) of HSA and nitrous oxide (N2O). The stoichiometry for this reaction, viz., 1 mol of HSA sulfhydryl oxidized to 1 mol of N2O produced, is consistent with a net two-electron oxidation of the protein thiol to a sulfenic acid. The sulfenic acid product of HSA was shown to react with dimedone and GSH, two known reactions of sulfenic acids. In contrast, anaerobic oxidation of GSH and DTT by NO gave a stoichiometry close to the expected ratio of 2:1 (sulfhydryl oxidized to N2O produced) for the oxidation of these thiols to their disulfides and N2O. Under aerobic conditions, significant fractions of the sulfhydryl groups of HSA, GSH, and DTT were oxidized to their respective thionitrites, presumably by N2O3. Thionitrite formation was not observed in the absence of oxygen. The production of HSA-sulfenic acid by NO, as well as by other oxidizing agents such as H2O2 and peroxynitrite, followed by its reaction with circulating GSH or L-Cys may account for the mixed disulfides of HSA observed in plasma.
一氧化氮供体二乙胺硝普钠（DEA/NO）产生的一氧化氮（NO），在pH 7.4和37℃条件下，能迅速氧化人血清白蛋白（HSA）的游离巯基以及还原型谷胱甘肽（GSH）和二硫苏糖醇（DTT）的巯基。在厌氧条件下，NO氧化HSA巯基的主要产物是HSA的亚磺酸（RSOH）和一氧化二氮（N₂O）。该反应的化学计量关系，即1摩尔HSA巯基氧化生成1摩尔N₂O，与蛋白质巯基净两电子氧化为亚磺酸一致。已证明HSA的亚磺酸产物能与达美酮和GSH反应，这是亚磺酸的两个已知反应。相比之下，NO对GSH和DTT的厌氧氧化的化学计量关系接近预期的2:1比例（巯基氧化生成的N₂O），即这些巯基氧化为二硫化物和N₂O。在有氧条件下，HSA、GSH和DTT的巯基有很大一部分被氧化为各自的亚硝酸盐，推测是由N₂O₃所致。在无氧条件下未观察到亚硝酸盐的形成。NO以及其他氧化剂如H₂O₂和过氧亚硝酸根产生HSA-亚磺酸，随后其与循环中的GSH或L-半胱氨酸反应，可能是血浆中观察到的HSA混合二硫化物的原因。
