Ximenes Valdecir F, Fernandes João Roberto, Bueno Vânia B, Catalani Luiz H, de Oliveira Georgino H, Machado Rosângela G P
Departamento de Química, Faculdade de Ciências, Universidade Estadual Paulista, Bauru, Brazil.
J Pineal Res. 2007 Apr;42(3):291-6. doi: 10.1111/j.1600-079X.2007.00419.x.
There is a growing body of evidence that melatonin and its oxidation product, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), have anti-inflammatory properties. From a nutritional point of view, the discovery of melatonin in plant tissues emphasizes the importance of its relationship with plant peroxidases. Here we found that the pH of the reaction mixture has a profound influence in the reaction rate and products distribution when melatonin is oxidized by the plant enzyme horseradish peroxidase. At pH 5.5, 1 mm of melatonin was almost completely oxidized within 2 min, whereas only about 3% was consumed at pH 7.4. However, the relative yield of AFMK was higher in physiological pH. Radical-mediated oxidation products, including 2-hydroxymelatonin, a dimer of 2-hydroxymelatonin and O-demethylated dimer of melatonin account for the fast consumption of melatonin at pH 5.5. The higher production of AFMK at pH 7.4 was explained by the involvement of compound III of peroxidases as evidenced by spectral studies. On the other hand, the fast oxidative degradation at pH 5.5 was explained by the classic peroxidase cycle.
越来越多的证据表明，褪黑素及其氧化产物N(1)-乙酰-N(2)-甲酰基-5-甲氧基犬尿胺（AFMK）具有抗炎特性。从营养角度来看，在植物组织中发现褪黑素凸显了其与植物过氧化物酶关系的重要性。在此我们发现，当褪黑素被植物酶辣根过氧化物酶氧化时，反应混合物的pH值对反应速率和产物分布有深远影响。在pH 5.5时，1 mM的褪黑素在2分钟内几乎完全被氧化，而在pH 7.4时仅消耗约3%。然而，在生理pH值下AFMK的相对产率更高。自由基介导的氧化产物，包括2-羟基褪黑素、2-羟基褪黑素的二聚体和褪黑素的O-去甲基二聚体，是pH 5.5时褪黑素快速消耗的原因。光谱研究证明，过氧化物酶的化合物III参与其中，这解释了pH 7.4时AFMK产量较高的原因。另一方面，pH 5.5时的快速氧化降解是由经典的过氧化物酶循环解释的。
