Effect of chloride ion on the oxygen affinity of hemoglobin York (alpha 2 beta 2(146)Pro) and S-York hybrid hemoglobin (alpha 2 beta S beta York). Role of the beta 82 lysyl and beta 146 histydyl residues in chloride binding to hemoglobin.

We estimated the relative role of various chloride binding sites in determining the oxygen affinity of hemoglobin using abnormal hemoglobins such as Hb York (Hb Y) (alpha 2 beta 2(146)Pro), Hb Malmö (Hb M) (alpha 2 beta 2(97)Gln), and Hb S and chemically modified hemoglobins such as cross-linked Hb S, Hb Y, and asymmetrical SY hemoglobin with bis(3,5-dibromosalicyl)fumarate. The chloride effect on the p50 values of Hb S and Hb M was identical to that of Hb A. In contrast, the effect of chloride on the p50 values of Hb Y was only 20% of that of Hb A. Cross-linking between the two beta 82 lysyl residues with fumarate decreased the chloride effect by 40%. The effect of chloride on cross-linked Hb Y, in which both beta 82 lysyl and beta 146 histidyl residues were modified, was unchanged from that on Hb Y (20% of Hb A). The effect of chloride on the p50 value of SY asymmetrical hybrid hemoglobin was 40% of that of Hb A or Hb S, which is midway between the values obtained for cross-linked Hb S and Hb Y. From these results, the contribution of beta 146 His and beta 82 Lys on oxygen affinity by binding of chloride was calculated to be 40% each; the remaining 20% chloride effect was attributed to alpha 1 Val.