Conformational and functional properties of haemoglobin in water + alcohol mixtures. Dependence of bulk electrostatic and hydrophobic interactions upon pH and KCl concentration

Abstract

The reaction of haemoglobin with oxygen in the presence of some monohydric alcohols has been studied at various KCl concentrations and pH values.

The analysis of the results followed a previously described approach allowing: (1) the determination of the effects of cosolvents on the free-energy difference between T and R states of haemoglobin and (2) the separation of these effects into contributions linearly related to the variation of the inverse bulk dielectric constant of the water + cosolvent mixture (bulk-electrostatic contributions) and contributions that are ascribed to the variation of protein–solvent hydrophobic interactions (non-bulk-electrostatic contributions).

Bulk-electrostatic contributions were found to depend on pH and salt concentration.

Non-bulk-electrostatic contributions were also found to increase with increasing pH and salt concentration. Linear correlations, not dependent upon the particular alcohol, were found to connect the non-bulk-electrostatic contributions obtained at different KCl concentrations or pH values.