title: Myeloperoxidase-catalyzed oxidation of melatonin by activated neutrophils.
abstract: In the presence of hydrogen peroxide, horseradish peroxidase (HRP) catalyzes the production of N(1)-acetyl-N(2)-formyl-5-methoxykynuramine from melatonin. This reaction consumes oxygen and exhibits chemiluminescence in the 440-540 nm region. The excited cleavage product derived from the thermolysis of an intermediate dioxetane is suggested to be the emitting species. Chemiluminescence and the indole ring cleavage product were also observed when HRP/H(2)O(2) was replaced by phorbol myristate acetate or opsonized zymosan-activated neutrophils. Azide, a myeloperoxidase inhibitor, strongly suppressed melatonin oxidation. Superoxide dismutase has a strong inhibitory effect on light emission but catalase and uric acid are without effect on the emission. The oxidation of melatonin by activated neutrophils may be relevant to the in vivo functions of myeloperoxidase and melatonin. The possible biological implication of melatonin oxidation by neutrophils, especially in inflammatory conditions, is discussed.
authors: Departamento de Análises Clínicas e Toxicológicas, Faculdade de Ciências Farmacêuticas, São Paulo, CEP 05508-900, Brazil.
authors: S O
authors: SO
authors: Silva
authors: V F
authors: VF
authors: Ximenes
authors: L H
authors: LH
authors: Catalani
authors: A
authors: A
authors: Campa
mesh_terms: D002374:Catalase / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008163:Luminescent Measurements; D008550:Melatonin / Q000097:blood*; D018375:Neutrophil Activation; D009504:Neutrophils / Q000502:physiology*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000097:blood*; D013053:Spectrophotometry; D013482:Superoxide Dismutase / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D016166:Free Radical Scavengers; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D002374:Catalase; D009195:Peroxidase; D013482:Superoxide Dismutase; D008550:Melatonin; D013755:Tetradecanoylphorbol Acetate