Interaction of organic phosphates with bovine hemoglobin. I. Oxylabile and phosphate-labile proton binding

Adult bovine hemoglobin solutions were studied with respect to the influence of organic phosphates (adenosine-5'-triphosphate, 2,3-diphosphoglycerate, myo-inositolhexaphosphate) on the oxylabile proton binding (fixed-acid Haldane effect). At alkaline pH (less than 7.5) this Haldane effect is increased by organic phosphates, whereas at acid pH (less than 6.5) the effect is decreased; in the neutral pH range no unequivocal trend was found. The influence on the Haldane effect is caused by binding of organic phosphates to both deoxy- and liganded hemoglobin. The binding of 2,3-diphosphoglycerate and myo-inositolhexaphosphate causes a massive proton uptake. In going from deoxy- to liganded hemoglobin in the presence of organic phosphates the proton release due to phosphate release from deoxyhemoglobin and the proton uptake due to phosphate binding by liganded hemoglobin were shown to account for the phosphate-induced part of the fixed-acid Haldane effect.