[Stabilization of albumin by CaCl2- and MgCl2-regulated interaction of macromolecules: a study by the spin label method].

Effective thermodynamic activation parameters of spin-label transitions between microsurroundings in water-protein matrix of modified molecules of serum albumin are determined in 0.01 M acetate buffer, pH 5.6, in CaCl2 and MgCl2 concentration range from 10(-3) to 5 M and protein concentration 90-110 mg/ml. The "melting" of water-protein matrix being accompanied by disjoining pressure in water-protein matrix and native protein structure stability alterations is registered in the salt concentration range 0.1-0.3 M. The phenomena revealed are interpreted as phase transition from solution of protein clusters at the low salt concentrations to the "salting out" form of protein solution at high salt concentrations or to the solution in which interactions between proteins are stabilized by repulsive structural forces of residual hydration shells of the bound cations. This transition realizes through the intermediate (critical type) state characterized by weak protein-protein interactions. The flexibility of water-protein matrix and its permeability for the salt ions and water molecules is more pronounced in this region of moderate (approximately equal to 0.3 M) CaCl2 and MgCl2 concentrations.