Studies on the interactions between purified bovine caseins and alkaline-earth-metal ions.

1. Alkaline-earth-metal cations at low concentrations form soluble complexes with bovine caseins. The relative order of binding capacities is: Mg(2+)>Ca(2+)>Ba(2+)>Sr(2+). 2. The cations interact with both free ionized carboxyl groups of aspartic acid and glutamic acid and with monoester phosphate groups covalently bound to serine and threonine; at low concentrations of the cations interactions are predominantly with the phosphate groups. 3. The order of binding capacities for purified components of the casein complex is: alpha(s1)-casein>beta-casein>kappa-casein.