The effects of temperature and pH on the binding of ATP to carp (Cyprinus carpio) deoxyhemoglobin

The linkage relationships between the binding of protons, organic phosphate, and oxygen to hemoglobin are well documented phenomena. These interactions provide a model for the investigation of linkage equilibria. Since ATP is the major organic phosphate in the erythrocytes of many fish, the binding of ATP to a representative fish hemoglobin (Carp I) was investigated. In these studies, both temperature and pH were varied so that their effects on ATP binding could be elucidated. The experimental binding constants were fitted to an equation that included the two major ionizable forms of ATP present within the experimental pH range. The resultant fitted parameters indicate three protons are taken up as deoxyhemoglobin binds the fully ionized form to ATP while only two protons are bound for the partially ionized form. The enthalpy of binding (delta H), provides insight concerning the possible physiological and ecological significance of this phenomenon.