Zang L Y, Cosma G, Gardner H, Vallyathan V
Pathology and Physiology Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505-2888, USA.
Biochim Biophys Acta. 1998 Nov 27;1425(3):469-77. doi: 10.1016/s0304-4165(98)00099-3.
The direct effects of the neurohormone melatonin on reactive oxygen species (ROS) were investigated. Melatonin was found to inhibit DMPO-O-2 formation in a dose-dependent manner. At the level of 1. 7+/-0.07 mM, melatonin caused 50% inhibition of EPR signal intensity of DMPO-O-2 during the reaction of xanthine and xanthine oxidase. The reaction rate constant of melatonin with O2- was found to be 1.25+/-0.07x103 M-1 s-1. However, melatonin (up to 1.2 mM) did not exhibit significant effect toward OH radical, produced by the Fenton reaction. In addition, we found no evidence for the formation of the melatonin indolyl cation radical that presumably precedes conversion of melatonin to its stable N1-acetyl-N2-5-methoxykynuramine (AMK) metabolite following sequential reactions of melatonin with O2- and OH. On the other hand, melatonin was capable of scavenging H2O2 in a dose-dependent manner with an IC50=0.5+/-0.02 mM. The reaction rate constant of melatonin with H2O2 was found to be 2.52+/-0.19x105 M-1 s-1. Furthermore, melatonin was also found to inhibit 1O2-dependent 2,2,6,6-tetramethylpiperidine oxide (TEMPO) radical formation during rose bengal photodynamic reaction. The results suggest that melatonin's antioxidant properties, in part, may involve a direct effect on scavenging of ROS.
研究了神经激素褪黑素对活性氧（ROS）的直接作用。发现褪黑素以剂量依赖的方式抑制DMPO-O-2的形成。在1.7±0.07 mM的水平下，褪黑素在黄嘌呤和黄嘌呤氧化酶反应过程中使DMPO-O-2的EPR信号强度抑制50%。发现褪黑素与O2-的反应速率常数为1.25±0.07×103 M-1 s-1。然而，褪黑素（高达1.2 mM）对芬顿反应产生的OH自由基没有显著影响。此外，我们没有发现褪黑素吲哚阳离子自由基形成的证据，该自由基可能是褪黑素与O2-和OH依次反应后转化为其稳定的N1-乙酰-N2-5-甲氧基犬尿胺（AMK）代谢物之前的产物。另一方面，褪黑素能够以剂量依赖的方式清除H2O2，IC50 = 0.5±0.02 mM。发现褪黑素与H2O2的反应速率常数为2.52±0.19×105 M-1 s-1。此外，还发现褪黑素在孟加拉玫瑰红光动力反应过程中抑制1O2依赖性的2,2,6,6-四甲基哌啶氧化物（TEMPO）自由基形成。结果表明，褪黑素的抗氧化特性部分可能涉及对ROS清除的直接作用。
