RESONANCE RAMAN SCATTERING STUDIES OF THE QUATERNARY STRUCTURE TRANSITION IN HEMOGLOBIN.

The oxygen-binding energy difference, the free energy of cooperativity, is a thermodynamic property, and its location can be determined from an examination of the deoxygenated and liganded proteins in both their high affinity and low affinity structures. An assessment of the energetic differences between these four steady-state protein structures should elucidate which interactions contain the free energy of cooperativity. Resonance Raman scattering plays a very important role in determining these interactions, since it is a very sensitive probe of the bonds involving the heme group. By examining the resonance Raman spectrum of the heme in both quaternary structures in the liganded and in the deoxy forms, it may in principle be determined if the free energy of cooperativity is localized in any heme-protein interactions. Raman experiments of the quaternary structure transition have now been reported for both states of ligand binding as well as for methemoglobins. This paper summarizes that data and the inferences that may be drawn from them.