Abstract
Precise oxygen equilibrium curves of hemoglobin stripped of phosphates were determined at pH 7.4 and five different temperatures. The data were thermodynamically analyzed according to Adair's stepwise oxygenation theory and the allosteric model of Monod et al . Heat of oxygenation of Hb(O 2) 3 was significantly larger than that of Hb, indicating that the shape of oxygen equilibrium curve is not invariant with the change of temperature. The results do not support the idea that the cooperative effects are essentially entropic in nature, suggesting that the allosteric transition from the unliganded T-state to the unliganded R-state is an endothermic process, during which the hemoglobin molecule gains entropy.
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