Linkage of organic phosphates to oxygen binding in human hemoglobin at high concentrations.
We have performed high-precision oxygen binding studies on human hemoglobin tetramers in the presence of a series of limited, subsaturating amounts of the effector compounds 2,3-diphosphoglycerate (DPG) and inositol hexaphosphate (IHP). The use of thin-layer optical methods enabled the use of high hemoglobin concentrations, preventing complications arising from the dissociation of the tetramer into dimers. Model-independent, simultaneous analysis of all data for each effector demonstrated that the intrinsic oxygen binding characteristics of the molecule are in agreement with those determined in earlier high-precision studies [e.g., Gill, S. J., Di Cera, E., Doyle, M. L., Bishop, G. A., & Robert, C. H. (1987) Biochemistry 26, 3995-4002] and that the affinity of the tetramer for the tightly binding effector IHP changes most markedly between the second and fourth oxygen binding steps, perhaps indicating a large conformational change. The data were then analyzed by using the truncated allosteric model [Di Cera, E., Robert, C. H., & Gill, S. J. (1987) Biochemistry 26, 4003-4008], which is based on the hypothesis that a quaternary conformational change occurs in the hemoglobin tetramer before the third and fourth oxygen molecules bind.
Robert
C H
CH
Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215.
Fall
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Gill
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SJ
D019794:2,3-Diphosphoglycerate; D000494:Allosteric Regulation; D001665:Binding Sites; D004163:Diphosphoglyceric Acids / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D010833:Phytic Acid / Q000378:metabolism; D011487:Protein Conformation; D013816:Thermodynamics
D004163:Diphosphoglyceric Acids; D006454:Hemoglobins; D010710:Phosphates; D019794:2,3-Diphosphoglycerate; D010833:Phytic Acid; D010100:Oxygen