title: Influence of the R----T transition on the optical absorption and magnetic circular dichroism spectra of methemoglobin fluoride, aquomethemoglobin, and hydroxymethemoglobin.
abstract: From the observed absorption spectra of methemoglobin fluoride (metHbF) and hemoglobin monoxide (HbCO) and the magnetic circular dichoism (MCD) spectrum of HbCO, molecular quantities of the high-spin ferric heme group of metHbF and the MCD spectra of metHbF can be calculated [Rots, M. J. F., & Zandstra, P. J. (1982) Mol. Phys. 46, 1283]. In an essentially similar procedure and with the molecular quantities obtained for metHbF (in the quaternary R state), the contributions of the high-spin fractions to the absorption and MCD spectra of metHbF in the quaternary T structure and of aquo- and hydroxymethemoglobin (metHbH2O and metHbOH, respectively) in both the R and the T states are estimated. In these calculations, the energy of the iron egd orbital, which participates in the charge-transfer (CT) transitions, is used as an adjustable parameter. The changes in the absorption and MCD spectra of metHbF and metHbH2O upon the R----T transition are supposed to arise solely from the changes in the contributions of the high-spin fractions to the spectra, due to the change in energy of the iron egd orbital. The calculation shows that a decrease in the energy of the iron egd oribital of 0.017 and 0.008 eV for metHbF and metHbH2O, respectively, is likely, upon the R----T transition. The lowering of the egd orbital of the high-spin form of metHbOH is arbitrarily chosen as the average of these values. In the calculations for metHbOH, the increase of the high-spin fraction upon the R----T transition is taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D002942:Circular Dichroism; D008433:Mathematics; D008706:Methemoglobin / Q000031:analogs & derivatives*; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: C041160:methemoglobin fluoride; C024963:aquomethemoglobin; D008706:Methemoglobin