Oxidation of melatonin by carbonate radicals and chemiluminescence emitted during pyrrole ring cleavage.
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)(3)(-) enhanced chemiluminescence by more than 10-fold, indicating scavenging of carbonate radicals. In the presence of 10% dimethylsulfoxide (DMSO) or 1 m mannitol, HCO(3)(-)-dependent as well as independent light emissions were only partially inhibited. With regard to the stimulatory effect of HCO(3)(-), this implies a formation of carbonate radicals (CO)(3)(-) independent of hydroxyl (OH) 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(3)(-) may contribute to its protective potency.
Hardeland
Rüdiger
R
Institute of Zoology and Anthropology, University of Göttingen, Göttingen, Germany. rhardel@gwdg.de
Poeggeler
Burkhard
B
Niebergall
Robert
R
Zelosko
Veronika
V
D002254:Carbonates / Q000737:chemistry*; D007735:Kynuramine / Q000031:analogs & derivatives* / Q000737:chemistry; D008163:Luminescent Measurements; D008550:Melatonin / Q000737:chemistry*; D010084:Oxidation-Reduction; D011758:Pyrroles / Q000737:chemistry
D002254:Carbonates; D011758:Pyrroles; D007735:Kynuramine; C041550:N-acetyl-N-formyl-5-methoxykynurenamine; D008550:Melatonin