Melatonin prevents MPO heme destruction mediated by self-generated HOCl during steady state catalysis.

Fixed amount of MPO (1 μM) was incubated with fixed amount of Cl^- (100 mM) and increasing concentration of MLT (12–200 μM), and the reaction mixtures were incrementally received fixed amount of H₂O₂ (20 μM, total concentration of 180 μM). After reaction completion, the spectra of the reaction mixtures were scanned from 300–700 nm.