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EPR spectroscopy of nitrite complexes of methemoglobin.

dc.contributor.author Schwab, DE
dc.contributor.author Stamler, JS
dc.contributor.author Singel, DJ
dc.coverage.spatial United States
dc.date.accessioned 2011-06-21T17:25:55Z
dc.date.issued 2010-07-19
dc.identifier http://www.ncbi.nlm.nih.gov/pubmed/20666390
dc.identifier.uri https://hdl.handle.net/10161/4033
dc.description.abstract The chemical interplay of nitrogen oxides (NO's) with hemoglobin (Hb) has attracted considerable recent attention because of its potential significance in the mechanism of NO-related vasoactivity regulated by Hb. An important theme of this interplay-redox coupling in adducts of heme iron and NO's-has sparked renewed interest in fundamental studies of FeNO(x) coordination complexes. In this Article, we report combined UV-vis and comprehensive electron paramagnetic resonance (EPR) spectroscopic studies that address intriguing questions raised in recent studies of the structure and affinity of the nitrite ligand in complexes with Fe(III) in methemoglobin (metHb). EPR spectra of metHb/NO(2)(-) are found to exhibit a characteristic doubling in their sharper spectral features. Comparative EPR measurements at X- and S-band frequencies, and in D(2)O versus H(2)O, argue against the assignment of this splitting as hyperfine structure. Correlated changes in the EPR spectra with pH enable complete assignment of the spectrum as deriving from the overlap of two low-spin species with g values of 3.018, 2.122, 1.45 and 2.870, 2.304, 1.45 (values for samples at 20 K and pH 7.4 in phosphate-buffered saline). These g values are typical of g values found for other heme proteins with N-coordinated ligands in the binding pocket and are thus suggestive of N-nitro versus O-nitrito coordination. The positions and shapes of the spectral lines vary only slightly with temperature until motional averaging ensues at approximately 150 K. The pattern of motional averaging in the variable-temperature EPR spectra and EPR studies of Fe(III)NO(2)(-)/Fe(II)NO hybrids suggest that one of two species is present in both of the alpha and beta subunits, while the other is exclusive to the beta subunit. Our results also reconfirm that the affinity of nitrite for metHb is of millimolar magnitude, thereby making a direct role for nitrite in physiological hypoxic vasodilation difficult to justify.
dc.language eng
dc.language.iso en_US
dc.relation.ispartof Inorg Chem
dc.relation.isversionof 10.1021/ic902085s
dc.subject Coordination Complexes
dc.subject Electron Spin Resonance Spectroscopy
dc.subject Humans
dc.subject Hydrogen-Ion Concentration
dc.subject Methemoglobin
dc.subject Nitrites
dc.title EPR spectroscopy of nitrite complexes of methemoglobin.
dc.title.alternative
dc.type Journal article
dc.description.version Version of Record
duke.date.pubdate 2010-7-19
duke.description.issue 14
duke.description.volume 49
dc.relation.journal Inorganic chemistry
pubs.author-url http://www.ncbi.nlm.nih.gov/pubmed/20666390
pubs.begin-page 6330
pubs.end-page 6337
pubs.issue 14
pubs.organisational-group Clinical Science Departments
pubs.organisational-group Duke
pubs.organisational-group Medicine
pubs.organisational-group Medicine, Pulmonary, Allergy, and Critical Care Medicine
pubs.organisational-group School of Medicine
pubs.publication-status Published
pubs.volume 49
dc.identifier.eissn 1520-510X


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