LOW-FREQUENCY VIBRATIONAL-MODES OF OXYGENATED MYOGLOBIN, HEMOGLOBINS,AND MODIFIED DERIVATIVES

The low frequency resonance Raman spectra of the dioxygen adducts of m yoglobin, hemoglobin, its isolated subunits, mesoheme-substituted hemo globin, and several deuteriated heme derivatives are reported. The obs erved oxygen isotopic shifts are used to assign the iron-oxygen stretc hing (similar to 570 cm(-1)) and the heretofore unobserved delta(Fe-O- O) bending (similar to 420 cm(-1)) modes. Although the delta(Fe-O-O) i s not enhanced in the case of oxymyoglobin, it is observed for all the hemoglobin derivatives, its exact frequency being relatively invariab le among the derivatives. The lack of sensitivity to H2O/D2O buffer ex change is consistent with our previous interpretation of H2O/D2O-induc ed shifts of nu(O-O) in the resonance Raman spectra of dioxygen adduct s of cobalt-substituted heme proteins; namely, that those shifts are a ssociated with alterations in vibrational coupling of nu(O-O) with int ernal modes of proximal histidyl imidazole rather than to steric or el ectronic effects of H/D exchange at the active site. No evidence is ob tained for enhancement of the nu(Fe-N) stretching frequency of the lin kage between the heme iron and the imidazole group of the proximal his tidine.