The Binding of Divalent Ions to the Phosphoglycoprotein Phosvitin

Abstract

Studies of viscosity, optical rotatory dispersion and circular dichroism on the phosphoglycoprotein Phosvitin revealed that this protein in some of its properties resembles a polyelectrolyte (1,2). As pointed out previously, this is easily understood if one considers that fifty-four per cent of all amino acid residues of phosvitin are phosphorylated (3). At neutral pH, where two hydroxyls of each phosphate group are ionized, the net electronic charge corresponds to about one negative charge per amino acid residue. Furthermore, we have shown that the presence of monovalent ions has an effect on the optical rotatory dispersion and circular dichroism of phosvitin. Since in biological processes cations, especially divalent ions, play an important role in maintaining a well-defined conformation necessary for the catalytic activity of certain enzymes, the binding studies have been extended to divalent cations with the aid of equilibrium dialysis techniques. In addition, an investigation of the effect of ion binding on the conformational characteristics of this protein has been initiated using optical methods, i.e. optical rotatory dispersion and circular dichroism.