Kinetic and spectroscopic studies of haemoglobin and myoglobin from Urechis caupo. Distal residue effects

Heme rotational isomerism is not required for the production of Q-band splitting in the spectra of iron-porphyrin proteins

“…The observed splitting of the a band in the spectrum of MbmNO has been attributed to nondegeneracy of the eg(ir*x->,) orbitals of the porphyrin resulting from dxz, dyz nondegeneracy traced to the stereochemical influence of the distal histidine. [13][14][15] The absence of splitting in the a band of the HbcmNO spectrum is consistent with the absence of a distal histidine in this hemoglobin. A similar, though less pronounced splitting is seen for MbnCO, again in contrast with the HbcnCO analogue.…”

The Synthetic and Structural Chemistry of Heme Derivatives with Nitric Oxide Ligands

“…Early work showed that the reaction of iron(III) hemoproteins with NO generally led to iron(II) derivatives by reductive nitrosylation. Reduction rates for hemoglobin and myoglobin derivatives show significant variation, and recently, Ford et al have shown a pH dependency toward reductive nitrosylation. Nitrophorins from the kissing bug reversibly bind NO but remain in the iron(III) state under all conditions …”