Ion-binding properties of S-layer proteins from Bacillus subtilis

A study was made of K+, Na+, Ca++ and Mg++ binding and ion-exchange properties of S-layer proteins from Bacillus subtilis. Our results indicate that the proteins of S-layer have two binding sites with pK of 3.17 and 2.41. To study the capacity of S-layer subunits to bind K+, Na+, Ca++ and Mg++, potentiometric titrations were performed according to Albert on proteins in solution in the presence and the absence of cations. It appears that the proteins possess dissociable groups with different affinity for various cations.