title: H2O2/nitrite-induced post-translational modifications of human hemoglobin determined by mass spectrometry: redox regulation of tyrosine nitration and 3-nitrotyrosine reduction by antioxidants.
abstract: Covalent modifications of proteins by endogenous reactive nitrogen oxide species lead to cytotoxic effects that are implicated in diseases associated with chronic infections and inflammation. Tyrosine nitration is a major post-translational modification of proteins by reactive nitrogen oxide species. Recent studies suggest that nitrotyrosine is not a permanent protein modification. We previously demonstrated that lipoyl dehydrogenase is capable of converting 3-nitrotyrosine into 3-aminotyrosine in the presence of certain reducing agents. In this study, we compared the abilities of various hemoproteins, hemin, and the cobalt-containing cofactor cyanocobalamin to mediate H(2)O(2)/nitrite-dependent tyrosine nitration and found that these hemoproteins and metal-containing cofactors also catalyzed the reduction of 3-nitrotyrosine to various extents in the presence of thiol reducing agents or ascorbate. The H(2)O(2)/nitrite-induced post-translational modifications of human hemoglobin identified by nanoLC/nanospray ionization tandem mass spectrometric analysis of the tryptic digest include nitration of tyrosine and tryptophan, as well as oxidation of methionine and cysteine residues. Nitration of human hemoglobin by H(2)O(2)/nitrite was detected on Tyr24 and Tyr42 (alpha-chain) and on Tyr130 and Trp15 (beta-chain) in the alphabeta-dimer. Oxidation of methionine and cysteine residues was also observed. Furthermore, hemoglobin also catalyzed nitro reduction of 3-nitrotyrosine to form 3-aminotyrosine, at Tyr24 in the alpha-chain peptide of human Hb in the presence of ascorbate. The enhanced peroxidase activity of nitrated hemoglobin can be reversed by the antioxidant ascorbate. These results suggest a possible in vivo pathway for hemoglobin contributing to denitration of nitrated proteins through redox regulation.
authors.affiliation: Department of Chemistry and Biochemistry, National Chung Cheng University, 168 University Road, Chia-Yi 62142, Taiwan. chehjc@ccu.edu.tw
authors.forename: Hauh-Jyun Candy
authors.initials: HJ
authors.lastname: Chen
authors.forename: Chia-Ming
authors.initials: CM
authors.lastname: Chang
authors.forename: Wen-Peng
authors.initials: WP
authors.lastname: Lin
authors.forename: Dar-Long
authors.initials: DL
authors.lastname: Cheng
authors.forename: Mei-I
authors.initials: MI
authors.lastname: Leong
mesh_terms: D000595:Amino Acid Sequence; D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D006427:Hemin / Q000378:metabolism; D006454:Hemoglobins / Q000032:analysis / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008715:Methionine / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D026361:Reactive Nitrogen Species / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D014357:Trypsin / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism
chemical_list: D000975:Antioxidants; D006454:Hemoglobins; D009566:Nitrates; D009573:Nitrites; D026361:Reactive Nitrogen Species; C002744:3-nitrotyrosine; D014443:Tyrosine; D006427:Hemin; D008715:Methionine; D006861:Hydrogen Peroxide; D009195:Peroxidase; D014357:Trypsin; D003545:Cysteine; D014805:Vitamin B 12; D001205:Ascorbic Acid