Comparison of the resonance Raman spectra of carbon monoxy and oxy hemoglobin and myoglobin: similarities and differences in heme electron distribution.

With 441.6-nm excitation, which is near the Soret band, we observe that the resonance Raman spectra of hemoproteins contain not only the bands between 650 and 1700 cm-1 which arise from vibrations of the conjugated macrocycle, but also bands below 650 cm-1, some of which involve vibrations of the iron pyrrole-nitrogen bonds. The spectra of the oxygen and carbon monoxide complexes of both myoglobin and hemoglobin are sufficiently similar to those of low spin met derivatives, that the electronic distribution on the heme for both ligands can be interpreted as that of a low spin ferriheme. This agrees with an earlier interpretation, by others, of comparative optical absorption spectra and, as pointed out previously, would imply that in the complex the ligands are bound as O2- and CO-. However, band frequencies and relative intensities differ somewhat between the carbon monoxide and oxygen complexes of the same protein, which indicates differences between the details of the pi-electron distributions in the corresponding complexes.