Abstract
This paper reviews calorimetric results obtained on ligand binding reactions to various hemoglobins. A special gas-liquid microcalorimeter has been developed for these studies. Both liquid-liquid and gas-liquid titrations can be performed with the system. Application of this method has been made to determine the heats of CO(g) and IHP(aq) binding to a variety of hemoglobins under various conditions. Results for human hemoglobins normal A and M Iwate show differences due to allosteric changes and proton release values. The heats measured are sensitive to buffer and counterion species. Proper cognizance of these effects is needed in order to interpret the measured heat values. Calorimetric gas titrations have also been made to examine the heat of CO(g) ligation as a function of extent of reaction. In the case of Hb A, no discernible differences are found between 5 to 95% degree of saturation. However, hemoglobin Trout I shows a marked dependence of the heat of reaction with degree of saturation. A full analysis of the calorimetric results of Trout I in conjunction with binding curve data has allowed an optimal determination of stepwise equilibrium constants and enthalpies of reaction for this hemoglobin.
