Quinone reductase 2 (QR2, E.C. 1.10.99.2) is implicated in cell reactive oxygen species production. The catalytic activity of this enzyme is inhibited by 1 microM of melatonin. QR2 was identified as the third melatonin binding site (MT3). It is of major importance to understand the exact roles of melatonin and QR2 in oxidative stress. A fascinating possibility that melatonin could serve as a co-substrate or substrate of QR2 was hypothesized recently. In the current investigation, nuclear magnetic resonance studies of the QR2 catalytic reaction were performed, the results led us to conclude that, whatever the conditions, melatonin is not cleaved off to form N1-acetyl-N2-formyl-5-methoxykynurenine by a catalytically active QR2, very strongly indicating that melatonin is neither a substrate nor a co-substrate of this enzyme. Further studies are needed in order to better understand the relationship between MT3/QR2, melatonin and redox status of the cells, in order to better explain the anti-oxidant activities of melatonin at pharmacological concentrations (>1 microM).

中文翻译：

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MT3 / QR2褪黑激素结合位点不使用褪黑激素作为底物或共底物。

醌还原酶2（QR2，EC 1.10.99.2）与细胞活性氧的产生有关。1 microM褪黑素可抑制该酶的催化活性。QR2被确定为第三个褪黑激素结合位点（MT3）。了解褪黑素和QR2在氧化应激中的确切作用至关重要。最近假设褪黑激素可以作为QR2的共底物或底物的一种引人入胜的可能性。在当前的研究中，进行了QR2催化反应的核磁共振研究，结果使我们得出结论，无论何种条件，褪黑素都不会被催化裂解形成N1-乙酰基-N2-甲酰基-5-甲氧基尿氨酸激活QR2，非常有力地表明褪黑激素既不是该酶的底物也不是其共底物。