title: Reaction of hemoglobin with HOCl: mechanism of heme destruction and free iron release.
abstract: Hypochlorous acid (HOCl) is generated by myeloperoxidase using chloride and hydrogen peroxide as substrates. HOCl and its conjugate base (OCl(-)) bind to the heme moiety of hemoglobin (Hb) and generate a transient ferric species whose formation and decay kinetics indicate it can participate in protein aggregation and heme destruction along with subsequent free iron release. The oxidation of the Hb heme moiety by OCl(-) was accompanied by marked heme destruction as judged by the decrease in and subsequent flattening of the Soret absorbance peak at 405 nm. HOCl-mediated Hb heme depletion was confirmed by HPLC analysis and in-gel heme staining. Exposure of Hb to increasing concentrations of HOCl produced a number of porphyrin degradation products resulting from oxidative cleavage of one or more of the carbon-methene bridges of the tetrapyrrole ring, as identified by their characteristic HPLC fluorescence and LC-MS. A nonreducing denaturing SDS-PAGE showed several degrees of protein aggregation. Similarly, porphyrin degradation products were identified after exposure of red blood cells to increasing concentrations of HOCl, indicating biological relevance of this finding. This work provides a direct link between Hb heme destruction and subsequent free iron accumulation, as occurs under inflammatory conditions where HOCl is formed in substantial amounts.
authors.affiliation: Department of Obstetrics and Gynecology, The C.S. Mott Center for Human Growth and Development, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Dhiman
authors.initials: D
authors.lastname: Maitra
authors.forename: Jaeman
authors.initials: J
authors.lastname: Byun
authors.forename: Peter R
authors.initials: PR
authors.lastname: Andreana
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Abdulhamid
authors.forename: Michael P
authors.initials: MP
authors.lastname: Diamond
authors.forename: Ghassan M
authors.initials: GM
authors.lastname: Saed
authors.forename: Subramaniam
authors.initials: S
authors.lastname: Pennathur
authors.forename: Husam M
authors.initials: HM
authors.lastname: Abu-Soud
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006418:Heme / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry*; D006997:Hypochlorous Acid / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D013058:Mass Spectrometry; D013050:Spectrometry, Fluorescence
chemical_list: D006454:Hemoglobins; D006418:Heme; D006997:Hypochlorous Acid; D007501:Iron