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Abstract
Abstract The binding affinity to hemoglobin of 2,3-bisphosphoglycerate, ATP, and some other phosphorylated red cell metabolites has been measured at pH 7.2 in 0.12 m KCl to simulate physiological conditions. The dissociation constant with 2,3-bisphosphoglycerate is independent of hemoglobin concentration in the range 0.06 to 4 mm. There is one binding site per deoxyhemoglobin tetramer. Phosphorylated compounds bind weakly to one site per tetramer of oxyhemoglobin. Dissociation constants determined for 2,3-bisphosphoglycerate are 4.22 x 10-5 m at 22° and 1.03 x 10-4 m at 37° with deoxyhemoglobin and ∼2.5 x 10-3 m at 22° and 4.75 x 10-3 m at 37° with oxyhemoglobin. Dissociation constants for ATP are 8.54 x 10-5 m at 25° with deoxyhemoglobin and 2.55 x 10-3 m for oxyhemoglobin at 25°. Binding to ADP, 1,3-bisphosphoglycerate and glucose-1,6-P2 was measured. The dissociation constant for magnesium complexes of 2,3-bisphosphoglycerate to deoxyhemoglobin was too weak to measure (g 10-3 m at 37°); magnesium complexes of ATP have an apparent dissociation constant of 1.15 x 10-3 m at 25°. The effects of the differential binding of cellular intermediates on red cell glycolysis and 2,3-bisphosphoglycerate metabolism are discussed.
Highlights
2,3-bisphosphoglycerate is independent of hemoglobin concentration in the range 0.06 to 4 mM
Studies of the physiology of the phenomenon in human red cells have been concerned largely with t,he biochemistry of 2,3-bisphosphoglycerate (2,3-DPG), the soluble phosphate compound that occurs in highest concentration in these cells, approximately equivalent to hemoglobin in molarity
(e.g. see Refs. 8-10) or pathological conditions such as anemia [11]. These effects have been attributed to the release of inhibition of diphosphoglycerate mutase [12, 13] caused by the decrease in free 2,3-DPG that would result from its tight binding to deoxyhemoglobin
Summary
The binding affinity to hemoglobin of 2 ,J-bisphosphoglycerate, ATP, and some other phosphorylated red cell metabolites has been measured at pH 7.2 in 0.12 M KC1 to simulate physiological conditions. Phosphorylated compounds bind weakly to one site per tetramer of oxyhemoglobin. Dissociation constants for ATP are 8.54 X 10m5 M at 25” with deoxyhemoglobin and 2.55 X 10v3 M for oxyhemoglobin at 25”. The observation that certain phosphorylated red cell metabolites bind tightly to hemoglobin by Benesch et al [1, 2] and Chanutin and Curnish [3] has clarified many aspects of hemoglobin structure and function Studies of the physiology of the phenomenon in human red cells have been concerned largely with t,he biochemistry of 2,3-bisphosphoglycerate (2,3-DPG), the soluble phosphate compound that occurs in highest concentration in these cells, approximately equivalent to hemoglobin in molarity. Medical Sciences, CA-06927 and RR-05539 to this Institute, and by an appropriation from the Commonwealth of Pennsylvania
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