Binding of Calcium to Serum Albumin I. Stoichiometry and Intrinsic Association Constant at Physiological pH, Ionic Strength, and Temperature

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Abstract
Ultrafiltration and spectrophotometric methods have shown that calcium is bound reversibly to serum albumin by a single class of 12±1 identical, independent binding sites with an association constant = 90-100 litres/mole at 37 °C in unbuffered solutions with pH 7.4 and ionic strength 0.15–0.16. Tea. albumin, and calcium ion concentration were varied over 11-, 6-, and 88-fold ranges. Albumins prepared by different methods had the same affinity. An unrecognized high citrate content of purified albumin is shown to be a plausible cause of previous disparate binding results.