The interaction of sodium maleate with human haemoglobin.

We have studied the effect of sodium maleate on the reaction of haemoglobin with oxygen at various temperatures between 10 degrees C and 30 degrees C. At all the temperatures investigated, the presence of sodium maleate causes a significant increase of log p50. Analysis of the experimental data in terms of Wyman's linkage theory indicates that one oxygen-linked maleate molecule bound to the haemoglobin tetramer in the deoxy conformation is released when the tetramer is oxygenated. Further analysis within the framework of the Monod-Wyman-Changeux model, considering maleate as a classical allosteric inhibitor, enabled us to obtain the equilibrium constant for the binding of maleate to deoxyhaemoglobin at various temperatures and therefore the values of the standard binding entropy and enthalpy. These last values indicate that the binding of maleate to deoxyhaemoglobin is an exothermic enthalpy-driven process.