Binding of Calcium to Serum Albumin II. Effect of pH via Competitive Hydrogen and Calcium Ion Binding to the Imidazole Groups of Albumin

A study by an ultrafiltration method at 37 °C and ionic strength 0.15–0.16 has shown that binding of calcium to serum albumin in the pH region from 6.5 to 8.5 is adequately described by a competitive model, where hydrogen and calcium ions combine reversibly with 12 of the 16 imidazole groups of albumin with intrinsic association constants of 107.55and 241 litres/mole, respectively. Electrostatic correction to binding of calcium appears negligible.