The binding of CO2 to human hemoglobin

CO₂ dissociation curves of concentrated human deoxy and carbon monoxyhemoglobin at 37°, pH 7.6 to 7.0, pCO₂ = 10 to 160 mm Hg, have been obtained by a rapid mixing and ion exchange technique. The CO₂ dissociation curves for deoxyhemoglobin can only be fitted by assuming 2 classes of binding sites for carbon dioxide. The simplest way to account for the experimental data is to assume that the α amino groups of the α and β chains react with carbon dioxide with affinities that differ by at least a factor of 3. No difference in reactivity with CO₂ was found among the 4 terminal α amino groups of carbon monoxyhemoglobin.