Interaction of organic phosphates with bovine hemoglobin. II. Oxygen binding equilibria of newborn and adult hemoglobin

Abstract

We investigated oxylabile H+ binding and pH dependent oxygen binding of adult and newborn bovine hemoglobin as influenced by the organic phosphates 2,3-disphosphoglycerate (DPG), adenosine-5'-triphosphate (ATP), and myoinositol hexaphosphate (IHP). The oxygen affinity of newborn bovine hemoglobin is higher than that of adult hemoglobin over a pH over a pH range of 6.5 to 8. Both DPG and IHP decrease the oxygen affinity of adult bovine hemoglobin. IHP not only decreases the oxygen affinity, but also reduces the apparent cooperativity, whereas DPG does not affect cooperativity. The rise in logP50 upon addition of DPG is about equal for adult and newborn bovine hemoglobin: at pH 7.0 we find delta logP50 values of 0.14 and 0.13 respectively upon addition of a fivefold excess of organic phosphate. This agrees with the identical nature of the presumed organic phosphate binding site in these two hemoglobins, but contrasts with the situation in man: newborn human hemoglobin is much less influenced by organic phosphates than adult human hemoglobin.