Change in surface properties of hemoglobin induced by heme reaction with O2 and CO

Abstract

The surface properties of hemoglobin bound to O2 (HbO2) or CO (HbCO) were investigated by ethanol precipitation, particle size analysis, and ζ potential measurements. We found that, compared with HbO2, HbCO is surrounded by more hydration water molecules, resulting in the greater physicochemical stability of HbCO in aqueous conditions. The intermolecular interactions of HbO2 and HbCO were studied by acquiring atomic force microscopy images under ambient air conditions. HbCO molecules easily aggregated on the hydrophilic mica substrate compared with HbO2 molecules during the dewetting process. We discuss these results in terms of a competing process between dispersion forces and adsorption on the hydrophilic mica substrate. The observed results suggest that the local structural differences between Fe–O2 and Fe–CO influence the surface structure of the protein, leading to the observed dissimilar physicochemical properties of HbO2 and HbCO.