Oxidation of melatonin by carbonate radicals and chemiluminescence emitted during pyrrole ring cleavage
Article first published online: 17 DEC 2002
Journal of Pineal Research
Volume 34, Issue 1, pages 17–25, January 2003
How to Cite
Hardeland, R., Poeggeler, B., Niebergall, R. and Zelosko, V. (2003), Oxidation of melatonin by carbonate radicals and chemiluminescence emitted during pyrrole ring cleavage. Journal of Pineal Research, 34: 17–25. doi: 10.1034/j.1600-079X.2003.02941.x
- Issue published online: 17 DEC 2002
- Article first published online: 17 DEC 2002
- Received June 6, 2002; accepted August 14, 2002.
- N1-acetyl-N 2-formyl-5-methoxykynuramine;
- carbonate radicals;
- carbon dioxide radicals;
- superoxide anions
Abstract: Oxidation of melatonin was followed by measuring chemiluminescence emitted during pyrrole ring cleavage, a process leading to the main oxidation product of this indoleamine, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK). Radical reactions of melatonin were studied in two variants of a moderately alkaline (pH 8) H2O2 system, one of which contained hemin as a catalyst. In both systems, light emission from melatonin oxidation lasted several hours. Time courses and turnover rates depended on the presence or absence of hemin; the catalyst enhanced light emission many-fold. In the two reaction systems, the presence of hydrogen carbonate (HCO) enhanced chemiluminescence by more than 10-fold, indicating scavenging of carbonate radicals. In the presence of 10% dimethylsulfoxide (DMSO) or 1 m mannitol, HCO-dependent as well as independent light emissions were only partially inhibited. With regard to the stimulatory effect of HCO, this implies a formation of carbonate radicals () independent of hydroxyl (ḃOH) radicals, presumably involving superoxide anions abundantly present in the system. Tiron, a scavenger of superoxide anions, strongly and almost instantaneously inhibited chemiluminescence, in accordance to the requirement of this reactive oxygen species for AFMK formation and its involvement in -radical formation. Melatonin's capability of scavenging CO may contribute to its protective potency.