Li Haitao, Samouilov Alexandre, Liu Xiaoping, Zweier Jay L
Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute and Division of Cardiovascular Medicine, Department of Internal Medicine, Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
J Biol Chem. 2004 Apr 23;279(17):16939-46. doi: 10.1074/jbc.M314336200. Epub 2004 Feb 6.
Under anaerobic conditions, xanthine oxidase (XO)-catalyzed nitrite reduction can be an important source of nitric oxide (NO). However, questions remain regarding whether significant XO-mediated NO generation also occurs under aerobic conditions. Therefore, electron paramagnetic resonance, chemiluminescence NO-analyzer, and NO-electrode studies were performed to characterize the kinetics and magnitude of XO-mediated nitrite reduction as a function of oxygen tension. With substrates xanthine or 2,3-dihydroxybenz-aldehyde that provide electrons to XO at the molybdenum site, the rate of NO production followed Michaelis-Menten kinetics, and oxygen functioned as a competitive inhibitor of nitrite reduction. However, with flavin-adenine dinucleotide site-binding substrate NADH as electron donor, aerobic NO production was maintained at more than 70% of anaerobic levels, and binding of NADH to the flavin-adenine dinucleotide site seemed to prevent oxygen binding. Therefore, under aerobic conditions, NADH would be the main electron donor for XO-catalyzed NO production in tissues. Studies of the pH dependence of NO formation indicated that lower pH values decrease oxygen reduction but greatly increase nitrite reduction, facilitating NO generation. Isotope tracer studies demonstrated that XO-mediated NO formation occurs in normoxic and hypoxic heart tissue. Thus, XO-mediated NO generation occurs under aerobic conditions and is regulated by oxygen tension, pH, nitrite, and reducing substrate concentrations.
在厌氧条件下，黄嘌呤氧化酶（XO）催化的亚硝酸盐还原可能是一氧化氮（NO）的重要来源。然而，关于在有氧条件下是否也会发生显著的XO介导的NO生成，仍存在疑问。因此，进行了电子顺磁共振、化学发光NO分析仪和NO电极研究，以表征XO介导的亚硝酸盐还原的动力学和幅度作为氧张力的函数。使用在钼位点向XO提供电子的底物黄嘌呤或2,3 - 二羟基苯甲醛时，NO生成速率遵循米氏动力学，并且氧作为亚硝酸盐还原的竞争性抑制剂起作用。然而，以黄素腺嘌呤二核苷酸位点结合底物NADH作为电子供体时，有氧条件下的NO生成维持在厌氧水平的70%以上，并且NADH与黄素腺嘌呤二核苷酸位点的结合似乎阻止了氧的结合。因此，在有氧条件下，NADH将是组织中XO催化的NO生成的主要电子供体。对NO形成的pH依赖性研究表明，较低的pH值会降低氧还原，但会大大增加亚硝酸盐还原，促进NO生成。同位素示踪研究表明，XO介导的NO形成发生在常氧和低氧心脏组织中。因此，XO介导的NO生成在有氧条件下发生，并受氧张力、pH、亚硝酸盐和还原底物浓度的调节。
