Resonance Raman studies of hemoglobins reconstituted with mesoheme. Unperturbed iron-histidine stretching frequencies in a functionally altered hemoglobin.

Hybrid hemoglobins, containing mesoheme in one type of subunit and protoheme in the partner subunits, have been studied by resonance Raman spectroscopy. These hybrids have been studied in both the met hybrid and fully reduced, deoxy forms. Judicious choice of laser excitation frequency permits selective enhancement of modes associated with each type of subunit; i.e., either meso- or protoheme-containing subunit. The assignments of low-frequency modes of meso- and protoheme are briefly discussed with special reference to the iron-histidine linkage. Despite functional differences between the hybrids, no significant changes in the strength of the iron-histidine linkages are detected by resonance Raman spectroscopy. These results are discussed with reference to recent high-resolution NMR studies of these same hybrids.