Binding of Calcium to Serum Albumin III. Influence of Ionic Strength and Ionic Medium

Abstract

A marked inverse relation between calcium binding to serum albumin and ionic strength has been demonstrated by means of an ultrafiltration method and shown to be identical in NaCl and KCl medium, while magnesium binds competitively to albumin with the same affinity as calcium ions. The ionic strength dependence has been resolved into a linear relation between log calcium ion activity coefficient and log apparent intrinsic association constant, whose extrapolated value at zero ionic strength of supporting electrolyte is 1445 ± 67 litres/mole. The importance of constant ionic strength in binding studies is emphasized.

Key Words:

• Calcium ions
• ionic medium
• ionic strength
• magnesium ions
• potassium ions
• protein binding
• serum albumin
• sodium ions
• ultrafiltration