Nitrite coordination in myoglobin
SourceJournal of inorganic biochemistry
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The coordination of nitrite in myoglobin (Mb) has been characterized by resonance Raman spectroscopy and the frequencies of the nitrite bound to the heme Fe as well to the 2-vinyl have been computed by density functional theory (DFT) calculations. The DFT Natural Bond Orbital (NBO) analysis and the extensive isotope-labeling in the resonance Raman experiments indicate that NO2 − (O1[sbnd]N[dbnd]O2) is bound to the heme Fe via O1. Based on the vibrational characterization of the reversible transition between low and high spin Fe[sbnd]O[sbnd]N[dbnd]O/2-nitrovinyl species, we suggest that the key step that triggers the spin-change is the increase of the proximal Fe[sbnd]NHis93 bond length. The frequencies of the O and N sensitive bands of the Fe[sbnd]O[sbnd]N[dbnd]O/2-nitrovinyl species remained largely unchanged in the low- to high-spin transition. Therefore the “greening” process in the reaction of ferric Mb with NO2 − proceeds through the Fe[sbnd]O[sbnd]N[dbnd]O/2-nitrovinyl species, which can exist in either the high or low-spin state. © 2016 Elsevier Inc.