title: Reduction of ferrylmyoglobin and ferrylhemoglobin by nitric oxide: a protective mechanism against ferryl hemoprotein-induced oxidations.
abstract: The reactions of metmyoglobin (metMb) and methemoglobin (metHb), oxidized to their respective oxoferryl free radical species (.Mb-FeIV = O/.Hb-4FeIV = O) by tert-butyl hydroperoxide (t-BuOOH), with nitric oxide (NO.) were studied by a combination of optical, electron spin resonance (ESR), ionspray mass (MS), fluorescence, and chemiluminescence spectrometries to gain insight into the mechanism by which NO. protects against oxidative injury produced by .Mb-FeIV = O/.Hb-4FeIV = O. Oxidation of metMb/metHb by t-BuOOH in a nitrogen atmosphere proceeded via the formation of two protein electrophilic centers, which were heme oxoferryl and the apoprotein radical centered at tyrosine (for the .Mb-FeIV = O form, the g value was calculated to be 2.0057), and was accompanied by the formation of t-BuOOH-derived tert-butyl(per)oxyl radicals. We hypothesized that NO. may reduce both oxoferryl and apoprotein free radical electrophilic centers of .Mb-FeIV = O/.Hb-4FeIV = O and eliminate tert-butyl(per)oxyl radicals, thus protecting against oxidative damage. We found that NO. reduced .Mb-FeIV = O/.Hb-4FeIV = O to their respective ferric (met) forms and prevented the following: (i) oxidation of cis-parinaric acid (PnA) in liposomes, (ii) oxidation of luminol, and (iii) formation of the tert-butyl(per)oxyl adduct with the spin trap DMPO. NO. eliminated the signals of tyrosyl radical detected by ESR and oxoferryl detected by MS in the reaction of t-BuOOH with metMb. As evidenced by MS of apomyoglobin, this effect was due to the two-electron reduction of .Mb-FeIV = O by NO. at the oxoferryl center rather than to nitrosylation of the tyrosine residues. Results of our in vitro experiments suggest that NO. exhibits a potent, targetable antioxidant effect against oxidative damage produced by oxoferryl Mb/Hb.
authors.affiliation: Department of Respiratory Research, Walter Reed Army Institute of Research, Washington, DC 20307, USA.
authors.forename: N V
authors.initials: NV
authors.lastname: Gorbunov
authors.forename: A N
authors.initials: AN
authors.lastname: Osipov
authors.forename: B W
authors.initials: BW
authors.lastname: Day
authors.forename: B
authors.initials: B
authors.lastname: Zayas-Rivera
authors.forename: V E
authors.initials: VE
authors.lastname: Kagan
authors.forename: N M
authors.initials: NM
authors.lastname: Elsayed
mesh_terms: D000818:Animals; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D006736:Horses; D006801:Humans; D007501:Iron / Q000737:chemistry*; D015227:Lipid Peroxidation / Q000187:drug effects; D008163:Luminescent Measurements; D008165:Luminol; D013058:Mass Spectrometry; D008706:Methemoglobin / Q000737:chemistry*; D008786:Metmyoglobin / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry* / Q000494:pharmacology; D010545:Peroxides / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013113:Spin Labels; D020122:tert-Butylhydroperoxide
chemical_list: D003497:Cyclic N-Oxides; D010545:Peroxides; D013113:Spin Labels; C028048:ferrylmyoglobin; D008786:Metmyoglobin; D009569:Nitric Oxide; D008165:Luminol; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D008706:Methemoglobin; D020122:tert-Butylhydroperoxide; D007501:Iron