Magnetic resonance studies of the binding of ^(13)C-labeled carbon monoxide to myoglobins and hemoglobins containing modified hemes

Abstract

The effects of changes in the groups attached to the periphery of the porphyrin ring of the heme of various hemoglobins and myoglobins on the environment experienced by the ligand, carbon monoxide, have been studied by observation of the chemical shift of the bound ^(13)CO. The results indicate that the major interaction between bound ligand and substituents around the porphyrin is that transmitted electronically from substituent to ligand. The nature of the protein environment around the ligand and the interaction between the proximal histidine (F8) and the ligand (through the iron atom) impose differences between subunits of hemoglobin and between myoglobins and hemoglobins which are largely, but not entirely, independent of these substituent effects. To assess the influence of protein structure on the chemical shifts of bound ligand, the shifts of ^(13)CO bound to myoglobin and hemoglobins from a wide range of species have also been measured.