The Concentration Dependence of the Oxygen Affinity of Haemoglobin S

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Abstract
Summary. The effect of the concentration of haemoglobin S (Hb S) on its oxygen‐dissociation properties was studied using either reconstituted Hb‐S cells of different mean corpuscular haemoglobin concentrations (MCHCs) prepared by osmotic lysis, or cells in which Hb S is diluted by the presence of another haemoglobin. Only 4% (phosphate buffer) and 21%(bis Tris) of the low oxygen affinity of fresh Hb‐S cells was found to be due to their slightly elevated intracellular 2, 3‐DPG concentrations since when the cells were depleted of 2, 3‐DPG most of the low affinity remained. The low affinity showed a marked dependence upon haemoglobin concentration which was absent for 2, 3‐DPG‐depleted Hb‐A cells and, by extrapolation, the MCHC at which the oxygen affinities of the Hb‐S cells became identical to that of the Hb‐A cells was 14.5 g/dl in phosphate buffer and 13.1 g/dl in bis Tris. Both fresh and 2, 3‐DPG‐depleted cells containing another haemoglobin as well as Hb S (Hb‐SA, Hb‐SC and Hb‐SF cells) were also found to have low oxygen affinities provided that the intracellular Hb‐S concentration (MC(Hb‐S)C) was above a certain level. These also showed a strong dependence upon the MC(Hb‐S)C. The mean MC(Hb‐S)C at which the low oxygen affinities of the DPG‐depleted cells were abolished were 8.3 g/dl (phosphate) and 11.2 g/dl (bis Tris). Hb F in fresh Hb‐SF cells brought about a much greater increase in oxygen affinity than the same amount of either Hb A or Hb C. In 2, 3‐DPG depleted cells Hb A showed a greater ability to ‘dilute’ the Hb S than did Hb C. The conditions for the low oxygen affinity of Hb S were therefore found to be very similar to those required for the gelling of both pure Hb S, and Hb S in haemoglobin mixtures. It was concluded therefore that the low oxygen affinity of the Hb S was caused by the polymerization and that the difference between the oxygen affinities of Hb‐S and Hb‐A cells may be used as a measure of the polymerization process.