title: Thionitroxides, RSNHO*: the structure of the SNO moiety in "S-Nitrosohemoglobin", a possible NO reservoir and transporter.
abstract: Nitric oxide (NO) plays important roles in many biological processes. S-Nitrosothiols have long been believed to have significant roles in NO biochemistry. The modified cysteine residue of hemoglobin was previously identified as a distorted S-nitrosothiol (RSNO) or an S-hydroxyamino radical (RSN*OH). Here we show that a thionitroxide (RSNHO*, S-aminyloxyl radical) is likely the observed species. Computational studies show that the thionitroxide is the only structure consistent with the electron density in the hemoglobin Cysbeta93-SNO structure previously reported. Although a metastable adduct, the thionitroxide in a hydrogen-bonding environment can form readily and release NO upon exposure to an aqueous environment. The thionitroxides could be responsible for the biological effects attributed to S-nitrosothiols or could serve as precursors to S-nitrosothiols in oxidative conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors.forename: Yi-Lei
authors.initials: YL
authors.lastname: Zhao
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D018360:Crystallography, X-Ray; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry* / Q000378:metabolism; D009589:Nitrogen Oxides / Q000737:chemistry / Q000378:metabolism; D011789:Quantum Theory; D026403:S-Nitrosothiols / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D006454:Hemoglobins; D009589:Nitrogen Oxides; D026403:S-Nitrosothiols; C103574:S-nitrosohemoglobin; D009569:Nitric Oxide; C039900:nitroxyl