Kharitonov V G, Sundquist A R, Sharma V S
Department of Medicine, University of California, San Diego, La Jolla 92093-0652, USA.
J Biol Chem. 1995 Nov 24;270(47):28158-64. doi: 10.1074/jbc.270.47.28158.
Nitrosothiols are powerful vasodilators. They act by releasing nitric oxide, which activates the heme protein guanylate cyclase. We have studied the kinetics of nitrosothiol formation of glutathione, cysteine, N-acetylcysteine, human serum albumin, and bovine serum albumin upon reaction with nitric oxide (NO) in the presence of oxygen. These studies have been made at low pH as well as at physiological pH. At pH 7.0, contrary to published reports, nitric oxide by itself does not react with thiols to yield nitrosothiol. However, formation of nitrosothiols is observed in the presence of oxygen. For all thiols studied, the rates of nitrosothiol formation were first order in O2 concentration and second order in NO concentration and at lower concentrations (< 5 mM thiol) also depended on thiol concentrations. Analysis of the kinetic data indicated that the rate-limiting step was the reaction of NO with oxygen. Analysis of the reaction products suggest that the main nitrosating species is N2O3: RSH+N2O3-->RSNO+NO2- + H+. Rate constants for this reaction for glutathione and several other low molecular weight thiols are in the range of 3-1.5 x 10(5) M-1 s-1, and for human and bovine serum albumins 0.3 x 10(5) M-1 s-1 and 0.06 x 10(5) M-1 s-1, respectively. The data further indicate that the reaction rate of the nitrosating species N2O3 with thiols is competitive with its rate of hydrolysis. At physiological concentrations nitrosoglutathione formation represents a significant metabolic fate of N2O3, and at glutathione concentrations of 5 mM or higher almost all of N2O3 formed is consumed in nitrosation of glutathione. Implications of these results for in vivo nitrosation of thiols are discussed.
亚硝基硫醇是强效血管舒张剂。它们通过释放一氧化氮起作用，一氧化氮可激活血红素蛋白鸟苷酸环化酶。我们研究了谷胱甘肽、半胱氨酸、N - 乙酰半胱氨酸、人血清白蛋白和牛血清白蛋白在有氧条件下与一氧化氮（NO）反应形成亚硝基硫醇的动力学。这些研究在低pH值以及生理pH值条件下进行。在pH 7.0时，与已发表的报告相反，一氧化氮本身不与硫醇反应生成亚硝基硫醇。然而，在有氧存在的情况下可观察到亚硝基硫醇的形成。对于所有研究的硫醇，亚硝基硫醇形成的速率在氧气浓度上是一级反应，在一氧化氮浓度上是二级反应，并且在较低浓度（<5 mM硫醇）时也取决于硫醇浓度。动力学数据分析表明限速步骤是一氧化氮与氧气的反应。反应产物分析表明主要的亚硝化物种是N2O3：RSH + N2O3 --> RSNO + NO2- + H+。谷胱甘肽和其他几种低分子量硫醇此反应的速率常数在3 - 1.5×10(5) M-1 s-1范围内，人血清白蛋白和牛血清白蛋白的速率常数分别为0.3×10(5) M-1 s-1和0.06×10(5) M-1 s-1。数据进一步表明亚硝化物种N2O3与硫醇的反应速率与其水解速率存在竞争关系。在生理浓度下，亚硝基谷胱甘肽的形成代表了N2O3的一个重要代谢途径，并且在谷胱甘肽浓度为5 mM或更高时，几乎所有形成的N2O3都在谷胱甘肽的亚硝化过程中被消耗。讨论了这些结果对体内硫醇亚硝化的影响。
