Analysis of the mechanism by which melatonin inhibits human eosinophil peroxidase.

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Lu T, Galijasevic S, Abdulhamid I, Abu-Soud HM

Analysis of the mechanism by which melatonin inhibits human eosinophil peroxidase.

Br J Pharmacol. 2008 Jul;154(6):1308-17. doi: 10.1038/bjp.2008.173. Epub 2008 Jun 2.

PubMed ID

18516076 [ View in PubMed

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Abstract

BACKGROUND AND PURPOSE: Eosinophil peroxidase (EPO) catalyses the formation of oxidants implicated in the pathogenesis of various respiratory diseases including allergy and asthma. Mechanisms for inhibiting EPO, once released, are poorly understood. The aim of this work is to determine the mechanisms by which melatonin, a hormone produced in the brain by the pineal gland, inhibits the catalytic activity of EPO. EXPERIMENTAL APPROACH: We utilized H2O2-selective electrode and direct rapid kinetic measurements to determine the pathways by which melatonin inhibits human EPO. KEY RESULTS: In the presence of plasma levels of bromide (Br-), melatonin inactivates EPO at two different points in the classic peroxidase cycle. First, it binds to EPO and forms an inactive complex, melatonin-EPO-Br, which restricts access of H2O2 to the catalytic site of the oxidation enzyme. Second, melatonin competes with Br- and switches the reaction from a two electron (2e-) to a one electron (1e-) pathway allowing the enzyme to function with catalase-like activity. Melatonin is a bulky molecule and binds to the entrance of the EPO haem pocket (regulatory sites). Furthermore, Br- seems to enhance the affinity of this binding. In the absence of Br-, melatonin accelerated formation of EPO Compound II and its decay by serving as a 1e- substrate for EPO Compounds I and II. CONCLUSIONS AND IMPLICATIONS: The interplay between EPO and melatonin may have a broader implication in the function of several biological systems. This dual regulation by melatonin is unique and represents a new mechanism for melatonin to control EPO and its downstream inflammatory pathways.

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Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Melatonin	Eosinophil peroxidase	Protein	Humans	Unknown	Inhibitor	Details