Determination of CO orientation in myoglobin by Linear dichroism (LD) (CAT#: STEM-ST-0127-WXH)

Introduction

One mechanism by which heme proteins control active site reactivity is through interaction of distal pocket residues with exogenous ligands. In myoglobin (Mb), it is believed that energetically unfavorable steric interactions with distal pocket residues reduce the binding affinity of CO, while bound O2 is stabilized by a hydrogen bond with the distal histidine. The distal pocket interactions in MbCO have particular interest, due to the existence of conformational substates that are functionally distinct and can be identified by vibrational frequencies of the Fe-C-0 group. The relative populations of these substates can be controlled by experimental conditions including temperature, pressure, pH, and hydration. Spectroscopic and crystallographic evidence indicates that His64, which interacts with the bound ligand in the "closed" distal pocket states, is displaced from the heme pocket toward solvent in the "open" pocket state.
The orientation of the bound CO in Mb remains an unresolved issue, despite several crystallographic studies.