Enthalpy changes for hemoglobin-ligand interactions: revised calorimetric data

Recently we reported values for the succesive enthalpy changes for the four steps of oxygen binding by diphosphoglycerate-free adult human hemoglobin [Biochem. Biophys. Res. Comm., $\text{56}$, 555 (1974)]. Systematic errors in the data render these results invalid. New data shows that cooperativity prevents resolution of successive heats of reaction and only average heats are currently accessible. At pH 7.4 and 6^o we obtain: $\text{Δ}\text{H[}\text{1}\text{4}\text{Hb+O}{}_2\text{→}\text{1}\text{4}\text{Hb (O}{}_2\text{)}{}_4\text{]=?13.2±0.4}$, $\text{Δ}\text{H[}\text{1}\text{4}\text{Hb(O}{}_2\text{)}{}_4\text{+CO→}\text{1}\text{4}\text{Hb(CO)}{}_4\text{+O}{}_2\text{]=?4.0±0.1}$, $\text{Δ}\text{H[}\text{1}\text{4}\text{Hb+CO→}\text{1}\text{4}\text{Hb(CO)}{}_4\text{] =?17.7±0.4 kcal/mole}$ ligand. These data form a consistent thermodynamic cycle.