Reciprocal interaction of hemoglobin with oxygen and protons. The influence of allosteric polyanions

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Abstract
The interaction of 3 inositol esters, inositol hexaphosphate (IHP), inositol pentaphosphate (IPP) and inositol hexasulfate (IHS) with Hb [human] was investigated. The proton uptake method was used to obtain the 6 binding constants for deoxy- and oxyhemoglobin. These data combined with O2 binding curves over a range of cofactor concentrations were used to test theoretical and empirical equations relating the affinity of Hb for O2 and allosteric effectors. The Bohr and Haldane coefficients in the presence of inositol esters are unequal at low, but not at high, concentration of cofactors. The maximum value reached by both parameters increases with the number of negative charges on the polyanion. 2,3-Diphosphoglycerate (DPG) differs sharply from the inositol esters since even at high concentrations of this cofactor, the Haldane coefficient remains elevated. This is a reflection of the negligible affinity of DPG for HbO2.