The iron-proximal histidine linkage and protein control of oxygen binding in hemoglobin: A transient Raman study.

Using time resolved resonance Raman scattering, we have studied the iron-proximal histidine linkage in transient species of hemoglobin (Hb) occurring within nanoseconds (ns) or longer of photoinduced ligand dissociation. Under these conditions the protein structure surrounding the heme, although destabilized, is still characteristic of the initial ligand bound species. Our technique allows for a clear distinction between contributions to the tertiary structure (associated with the proximal histidine) originating from the quaternary state of the protein and from the degree of ligand binding at the heme.