A resonance Raman study of ligand binding geometry in Glycera dibranchiata carbonmonoxyhemoglobin

Using 12CO and 13CO liganded protein and 406 nm laser excitation, multiple stretching (upsilon(Fe-CO), upsilon(C-O)) and bending (delta(Fe-C-O)) modes have been identified in the resonance Raman spectra of monomeric and polymeric Glycera hemoglobins. While the monomer fraction Glycera dibranchiata hemoglobin has upsilon(Fe-CO) = 496 cm-1, two distinct upsilon(Fe-CO) modes are found at 498 cm-1 and 520 cm-1 for the polymeric protein fraction. Data for upsilon(Fe-CO) and upsilon(C-O) were employed in an isolated three-body oscillator calculation to obtain approximate values for the Fe-C-O bond angle of 175 +/- 5 degrees for one polymeric component and 160 +/- 5 degrees for both the monomer and the second identifiable polymeric component. The differences in ligand binding geometry between the Glycera hemoglobins and other hemeproteins can be used to rationalize the relatively high values of on and off rates exhibited by the Glycera hemoglobins.