The Binding of Chloride Ions to Ligated and Unligated Human Hemoglobin and Its Influence on the Bohr Effect

Abstract

The contribution of the interaction of chloride ions with deoxy and oxyhemoglobin to the Bohr effect can be described by a simple binding model. Applying this model to experimental data reveals that at physiological pH and ionic strength about half of the release of Bohr protons is due to a difference in chloride ion binding to deoxy‐ and oxyhemoglobin. The chloride‐independent part of the Bohr effect corresponds with the shift in pK which His‐146β shows upon oxygenation. The proton absorption by hemoglobin observed upon oxygenation below pH 6 is apparently due to a chloride‐ion‐induced proton uptake, which is larger for oxyhemoglobin than for deoxyhemoglobin. The analysis of the experimental data indicates the existence of only two oxygen‐linked chloride ion binding sites in both deoxy and oxyhemoglobin. In deoxyhemoglobin the binding sites most likely consist of Val‐1α of one chain and Arg‐141α of the partner chain. The sites in oxyhemoglobin consist of groups with a pK value in the neutral pH range; they do not contain lysyl or arginyl residues. Copyright © 1979, Wiley Blackwell. All rights reserved