Melatonin prevents HOCl mediated MPO heme destruction and subsequent free iron release during MPO catalysis.

<p>MPO (1.2 μM) was incubated with 100 mM Cl⁻ in the absence and presence of 400 μM MLT followed by the addition of aliquots of H₂O₂ (in increments of 20 μM) to the reaction mixture. The free iron released was measured using ferrozine assay as detailed under Materials and methods. No free iron was detected before the addition of H₂O₂. The data are the averages of three independent experiments with the error bars representing the standard error of measurement.