title: Evidence for multiple differing cation binding sites on hemoglobin A and S.
abstract: Some divalent cations (at 10(-3)M concentration) have been shown to act as oxygen-linked ligands. The effect of Ca++ (only on hemoglobin S) and Zn++ (on normal hemoglobin and hemoglobin S) can be traced to a preferential binding of these cations to the oxy- conformation of the proteins; the reverse is true for Ni++, since its presence reduces the oxygen affinity of both hemoglobins. The results suggest: i) the existence of at least two different cation binding sites on hemoglobin; ii) the replacement of glutamic acid by valine in hemoglobins S introduces sufficient structural modification to form a new cation binding site.
mesh_terms: D001665:Binding Sites; D002413:Cations, Divalent / Q000378:metabolism*; D002942:Circular Dichroism; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D006441:Hemoglobin A / Q000378:metabolism*; D006451:Hemoglobin, Sickle / Q000378:metabolism*; D006801:Humans; D010101:Oxygen Consumption / Q000187:drug effects; D011487:Protein Conformation; D014633:Valine / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D005971:Glutamates; D006451:Hemoglobin, Sickle; D018698:Glutamic Acid; D006441:Hemoglobin A; D014633:Valine