2,3-DIPHOSPHOGLYCERATE BINDING OF ZN-2+ AND AL-3+

The blood red cell contains millimolar amounts of 2,3-diphosphoglycerate, yet no metal ion stability constants appear to have been determined. We show that in the free ligand the 2-phospho group is about six times more basic than the 3-phospho group. We have determined the stability constants for the binding of Zn2+ which occurs at about 0.2 mM in the red cell, and of Al3+ which reduces red cell size and inhibits haemoglobin synthesis. At physiological pH both metal ions occur predominantly as MA2 complexes. The free Zn2+ concentration permitted within the red cell by the 2:1 complex is about 0.3 μm. 2,3-Diphosphoglycerate binds Al3+ strongly enough so that at equilibrium there should be comparable concentrations of Al3+ on both sides of the red cell membrane. © 1990.