A 35Cl(-)-NMR study of the singular anion-binding properties of dromedary hemoglobin

35Cl(-)-NMR measurements of chloride binding to carbonmonoxy- and deoxy-dromedary hemoglobin reveal the existence of two classes of chloride-binding sites, one of high and the other of low affinity. Although this situation resembles that described for human hemoglobin, it was found that the number of binding sites as well as the association equilibrium constant for chloride binding are significantly higher in the dromedary protein. This difference may be due to the greater number of basic residues exposed to solvent and to the higher flexibility of dromedary hemoglobin. The two oxygen-linked polyanion-binding sites characteristic of this hemoglobin show competition for some of the high-affinity chloride-binding sites in keeping with their location in the cleft enclosed by the beta chains and between the alpha chains termini. It is suggested that the observed anion-binding properties of dromedary hemoglobin may contribute to the control of the physiological osmotic shock after rehydration.