Quaternary structures and low frequency molecular vibrations of haems of deoxy and oxyhaemoglobin studied by resonance Raman scattering

The influence of quaternary structure on the low frequency molecular vibrations of the haem within deoxyhaemoglobin (deoxy Hb) and Oxyhaemoglobin (oxy Hb) was studied by resonance Raman scattering. The FeO₂ stretching frequency was essentially identical between the high affinity (R) state (Hb A) and low affinity (T) state (Hb Kansas and Hb M Milwaukee with inositol hexaphosphate). However in deoxy Hb, only one of the polarized lines showed an appreciable frequency shift upon switch of quaternary structure, i.e. 215 to 218 cm^?1 for the T state (Hb A, des-His(146β) Hb, and des-Arg(141α) Hb (pH 6.5)) and 220 to 221 cm^?1 for the R state (des-Arg(141α) Hb (pH 9.0), des-His(146β)-Arg(141α) Hb and NES des-Arg(141α) Hb). Based on the observed ⁵⁴Fe isotopic frequency shift of the corresponding Raman lines of deoxy Hb A (214 → 217 cm^?1), of deoxy NES des-Arg Hb (220 → 223 cm^?1), of the protoporphyrinato-Fe(II)-(2-methylimidazole) complex in the ferrous high spin state (207 → 211 cm^?1) and of deoxymyoglobin (220 → 222 cm^?1) (Kitagawa et al., 1979), and on substitution of perdeuterated for protonated 2-methylimidazole in the deoxygenated picket fence complex (T_pivPP)Fe²⁺ (2-MeIm) (209 → 206 cm^?1), and on the results of normal co-ordinates calculation carried out previously, we proposed that the 216 cm^?1 line of deoxy Hb is associated primarily with the FeN_ε(HisF8) stretching mode and accordingly that the FeN_ε(HisF8) bond is stretched in the T state due to a strain exerted by globin.