Effect of polyanions on the kinetics of the reaction of apohemoglobin with carbonmonoxy heme.

The reaction of apohemoglobin with carbonmonoxy heme and with carbonmonoxy heme dimethyl ester was investigated in the presence and absence of inositol hexaphosphate. The binding stoichiometry of both heme derivatives to apohemoglobin was not affected by the presence of the polyphosphate, while, in both cases, the overall rate of recombination was substantially decreased. The absence of the negatively charged carboxyl groups in the dimethyl ester derivative of the heme indicated that the effect of inositol hexaphosphate on the reaction of apohemoglobin with heme was not due to electrostatic repulsions and resulted from conformational changes occurring upon the interaction of apohemoglobin with inositol hexaphosphate. Qualitative treatment of the kinetic data suggests that these conformational changes destabilize the intermediates of the reaction by increasing their redissociation into the original components. Also, benzenehexacarboxylate produced conformational changes in apohemoglobin and decreased its rate of reaction with carbonmonoxy heme, proving the aspecificity of the interaction of apohemoglobin with polyanions.