OXYGENATION OF HEMOGLOBIN IN PRESENCE OF 2,3-DIPHOSPHOGLYCERATE . EFFECT OF TEMPERATURE PH IONIC STRENGTH AND HEMOGLOBIN CONCENTRATION

The interaction of 2,3-diphosphoglycerate with hemoglobin is markedly influenced by environmental factors. The strength and extent of binding is inversely proportional to pH, as would be expected for electrostatic interaction with a polyanion. The effect of 2,3-diphosphoglycerate in lowering the oxygen affinity of hemoglobin can be regarded as a special salt effect, since neutral salts act similarly, albeit in concentrations 1000 times greater than 2,3-diphosphoglycerate. This molecule is thus capable of regulating oxygen affinity at the millimolar concentrations in which it occurs in the erythrocyte without disturbing the osmotic equilibrium. Both oxygen and 2,3-diphosphoglycerate binding by hemoglobin are exothermic. Since oxygenation involves displacement of 2,3-diphosphoglycerate, the temperature dependence of the oxygenation reaction is lowered in the presence of the phosphate cofactor, permitting correct oxygen release over a wider range of temperature. The reaction of 2,3-diphosphoglycerate with deoxyhemoglobin is accompanied by a decrease in entropy, which, together with other evidence, bears out the previously proposed model for the interaction of 2,3-diphosphoglycerate with hemoglobin. © 1969, American Chemical Society. All rights reserved.