Influence of quaternary structure on the state of the haem in carp and human methaemoglobins studied by resonance Raman scattering.

the resonance Raman spectra of carp and human methaemoglobin (metHb) derivatives in the T and R quaternary structures were measured in the frequency regions of 1200-1700 cm-1 and 100-600 cm-1. Conversion of carp and human fluoro metHb's to the T structure was accompanied by a frequency shift of the Raman line at 348 cm-1 to lower frequency by 5 cm-1, but all other lines were unaffected by the R-T transition. As the 348 cm-1 line was assigned to a porphyrin mode (v8) involving a bending motion of peripheral groups, the frequency change may be attributable to a change in van der Waals' interaction between haem and globin. On addition of inositol hexaphosphate to carp azide metHb, the intensity ratios of Raman lines (cm-1/cm-1), 1588/1567, 1641/1606, and 349/377, decreased. This indicates a shift of the high-spin/low-spin equilibrium towards high-spin side, in agreement with the rise in magnetic susceptibility. No distinct change was detected for the Raman spectra of aquo and cyano met Hb's on the R-T transition, even in the lower frequency region.