Hemoglobin-oxygen equilibrium at different hemoglobin and 2,3-diphosphoglycerate concentrations.
Hemoglobin-oxygen equilibrium curves at constant pH, ionic strength, and temperature were determined (a) on 2,3-DPG-free solutions at various hemoglobin (Hb) concentrations, (b) on solutions at various Hb concentrations but constant 2,3-DPG/Hb molar ratio, (c) on solutions at constant hemoglobin concentration but various 2,3-DPG/Hb molar ratios, and (d) on hemolysates at various Hb concentrations. Under all conditions the shape of the equilibrium curve was the same (n = 2.62 +/- 0.04, 33 experiments). Half-saturation pressure (P 1/2) did not change with increasing Hb concentration in case (a), whereas P 1/2 was linearly related to Hb concentration in case (b). In case (c) at 200 g/l Hb, P 1/2 increased sharply as 2,3-DPG/Hb molar ratio increased up to 0.4 but changed little as the ratio was further increased up to 1.5. This behavior is very different from that observed in diluted (5 g/l) solutions. P 1/2 of the hemolysates was also linearly related to Hb concentration but the slope was about twice that for case (b). These results cannot be explained by linked function theory or by a dimer-tetramer equilibrium. It is suggested that intermolecular interactions in the presence of organic phosphates may be responsible for the observed changes in Hb affinity for oxygen.
D003911:Dextrans / Q000494:pharmacology; D004163:Diphosphoglyceric Acids / Q000097:blood*; D006454:Hemoglobins / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D008024:Ligands; D008970:Molecular Weight; D010100:Oxygen / Q000097:blood*; D011205:Povidone / Q000494:pharmacology
D003911:Dextrans; D004163:Diphosphoglyceric Acids; D006454:Hemoglobins; D008024:Ligands; D011205:Povidone; D010100:Oxygen