The melatonin metabolite N-acetyl-5-methoxykynuramine is a potent singlet oxygen scavenger.
Singlet oxygen was generated by means of rose bengal under irradiation by visible light. N(1)-acetyl-5-methoxykynuramine (AMK) was rapidly destroyed by this reactive oxygen species, whereas its formylated precursor, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), was remarkably inert. At photon fluence rates of 1400 mumol photons/m(2)s, and using 20 mum rose bengal, most of initially 0.2 mm AMK was destroyed within 2 min, whereas AFMK remained practically unchanged for much longer periods of time. Competition experiments with other scavengers revealed the following order of reactivity towards singlet oxygen: diazabicyclo-[2,2,2]-octane (DABCO) << imidazole < 4-ethylphenol < N(alpha)-acetylhistidine < histidine < melatonin < AMK, the last one being about 150 times more effective than DABCO. Contrary to the oxidation in free radical-generating systems, AMK did not form adducts with the tyrosine side chain fragment, 4-ethylphenol, under the influence of singlet oxygen. In UV-exposed cells (keratinocytes, plant cells) it is likely to be more rapidly destroyed by singlet oxygen than formed from AFMK.
Schaefer
Meike
M
Johann Friedrich Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Göttingen, Germany.
Hardeland
Rüdiger
R
D001667:Binding, Competitive; D016166:Free Radical Scavengers / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D007735:Kynuramine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D008550:Melatonin / Q000737:chemistry / Q000378:metabolism*; D010879:Piperazines / Q000737:chemistry / Q000378:metabolism; D026082:Singlet Oxygen / Q000737:chemistry* / Q000378:metabolism; D013057:Spectrum Analysis
D016166:Free Radical Scavengers; D010879:Piperazines; D026082:Singlet Oxygen; D007735:Kynuramine; D006639:Histidine; C032131:N-acetyl-5-methoxy kynurenamine; D008550:Melatonin; C007306:triethylenediamine