The Binding of Calcium to _K-Casein and Para _K-Casein

Abstract

The binding of calcium to _K-casein and para _K-casein was studied by infrared spectra. The binding of calcium to the phosphoryl groups of _K-casein reached a plateau above 1m_M CaCl₂, and the binding to the carboxyl groups proceeded linearly up to 3m_M CaCl₂, and slowly above 3m_M CaCl₂, which were nearly identical to the results of _K-casein previously reported. The binding to carboxyl groups of para _K-casein proceeded similarly. The con-formational changes of _K-casein accompanying the bindings were determined by circular dichroism and ultraviolet spectra. The obtained results suggest that the hydrophobic sites of _K-casein are exposed to solvent without a change in secondary structure of the protein. Calcium promoted the dissolution of para _K-casein in the presence of urea.