title: Hemoglobins dioxygenate nitric oxide with high fidelity.
abstract: Distantly related members of the hemoglobin (Hb) superfamily including red blood cell Hb, muscle myoglobin (Mb) and the microbial flavohemoglobin (flavoHb) dioxygenate nitric oxide (.NO). The reaction serves important roles in .NO metabolism and detoxification throughout the aerobic biosphere. Analysis of the stoichiometric product nitrate shows greater than 99% double O-atom incorporation from Hb(18)O(2), Mb(18)O(2) and flavoHb(18)O(2) demonstrating a conserved high fidelity .NO dioxygenation mechanism. Whereas, reactions of .NO with the structurally unrelated Turbo cornutus MbO(2) or free superoxide radical (-O.(2)) yield sub-stoichiometric nitrate showing low fidelity O-atom incorporation. These and other results support a .NO dioxygenation mechanism involving (1) rapid reaction of .NO with a Fe(III-)O.(2) intermediate to form Fe(III-)OONO and (2) rapid isomerization of the Fe(III-)OONO intermediate to form nitrate. A sub-microsecond isomerization event is hypothesized in which the O-O bond homolyzes to form a protein caged [Fe(IV)O .NO(2)] intermediate and ferryl oxygen attacks .NO(2) to form nitrate. Hb functions as a .NO dioxygenase by controlling O(2) binding and electrochemistry, guiding .NO diffusion and reaction, and shielding highly reactive intermediates from solvent water and biomolecules.
authors.affiliation: Division of Critical Care Medicine, Children's Hospital Medical Center, 3333 Burnet Ave, MLC7006, Cincinnati, OH 45229, USA. paul.gardner@cchmc.org
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gardner
authors.forename: Anne M
authors.initials: AM
authors.lastname: Gardner
authors.forename: Wayne T
authors.initials: WT
authors.lastname: Brashear
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Suzuki
authors.forename: Angela N
authors.initials: AN
authors.lastname: Hvitved
authors.forename: Kenneth D R
authors.initials: KD
authors.lastname: Setchell
authors.forename: John S
authors.initials: JS
authors.lastname: Olson
mesh_terms: D000818:Animals; D002384:Catalysis; D004093:Dihydropteridine Reductase / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D006420:Hemeproteins / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000378:metabolism; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D009211:Myoglobin / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D050661:Sperm Whale / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D005290:Ferric Compounds; D006420:Hemeproteins; D006454:Hemoglobins; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D009211:Myoglobin; D009566:Nitrates; C066317:ferryl iron; D009569:Nitric Oxide; D007501:Iron; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases; D010100:Oxygen