title: Nitric oxide interactions with cobalamins: biochemical and functional consequences.
abstract: Nitric oxide (NO) is a paramagnetic gas that has been implicated in a wide range of biologic functions. The common pathway to evoke the functional response frequently involves the formation of an iron-nitrosyl complex in a target (heme) protein. In this study, we report on the interactions between NO and cobalt-containing vitamin B12 derivatives. Absorption spectroscopy showed that of the four Co(III) derivatives (cyanocobalamin [CN-Cbl], aquocobalamin [H2O-Cbl], adenosylcobalamin [Ado-Cbl], and methylcobalamin [MeCbl]), only the H2O-Cbl combined with NO. In addition, electron paramagnetic resonance spectroscopy of H2O-Cbl preparations showed the presence of a small amount of Cob-(II)alamin that was capable of combining with NO. The Co(III)-NO complex was very stable, but could transfer its NO moiety to hemoglobin (Hb). The transfer was accompanied by a reduction of the Co(III) to Co(II), indicating that NO+ (nitrosonium) was the leaving group. In accordance with this, the NO did not combine with the Hb Fe(II)-heme, but most likely with the Hb cysteine-thiolate. Similarly, the Co(III)-NO complex was capable of transferring its NO to glutathione. Ado-Cbl and Me-Cbl were susceptible to photolysis, but CN-Cbl and H2O-Cbl were not. The homolytic cleavage of the Co(III)-Ado or Co(III)-Me bond resulted in the reduction of the metal. When photolysis was performed in the presence of NO, formation of NO-Co(II) was observed. Co(II)-nitrosyl oxidized slowly to form Co(III)-nitrosyl. The capability of aquocobalamin to combine with NO had functional consequences. We found that nitrosylcobalamin had diminished ability to serve as a cofactor for the enzyme methionine synthase, and that aquocobalamin could quench NO-mediated inhibition of cell proliferation. Our in vitro studies therefore suggest that interactions between NO and cobalamins may have important consequences in vivo.
authors.affiliation: Duke University Marine Biomedical Center, Beaufort, NC, USA.
authors.forename: M
authors.initials: M
authors.lastname: Brouwer
authors.forename: W
authors.initials: W
authors.lastname: Chamulitrat
authors.forename: G
authors.initials: G
authors.lastname: Ferruzzi
authors.forename: D L
authors.initials: DL
authors.lastname: Sauls
authors.forename: J B
authors.initials: JB
authors.lastname: Weinberg
mesh_terms: D003038:Cobamides / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D018922:HL-60 Cells / Q000187:drug effects; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D006879:Hydroxocobalamin / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D013053:Spectrophotometry; D014805:Vitamin B 12 / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D003038:Cobamides; D006454:Hemoglobins; D009569:Nitric Oxide; C019476:mecobalamin; C000913:cobamamide; D014805:Vitamin B 12; D006879:Hydroxocobalamin