Coordination complexes and catalytic properties of proteins and related substances. 105. Electrostatic effects in hemoglobin: Bohr effect and ionic strength dependence of individual groups

Abstract

The electrostatic treatment applied in the preceding study to the titration behavior of individual groups in human deoxyhemoglobin and HbO2 was applied to the computation of the alkaline Bohr effect at various values of ionic strength. The enhanced proton binding of deoxyhemoglobin in the pH range of 6-9 was accounted for at ionic strength 0.01 M by the effects of the unique charge distributions of ionizable groups in the 2 quaternary states. At ionic strength 0.10 M the effects of 2-4 bound anions had to be considered in addition in the deoxyhemoglobin charge configuration. At the higher ionic strength 10 groups per tetramer contributed to the Bohr effect, whereas 28 groups were contributory at the lower ionic strength. The ionic strength dependence of individual groups in the 2 tetrameric structures as well as in the .alpha.-chain monomer was explained in terms of the electrostatic treatment. The differences in electrostatic behavior of deoxy- and HbO2 follow from particular dissymmetries in their configurations with respect to charge and static solvent accessibility.