[9] Measurement of protein-small ion interactions with ion-specific electrodes

This chapter provides a brief description of electrodes and their use in the study of the interaction of proteins with ions other than hydrogen. The introduction of membrane electrodes has led to varying degrees of success with this problem. The first and most prominent example has been the glass membrane electrode for hydrogen. Thus, a membrane electrode is composed of an ion-selective membrane, which has a fixed concentration of an appropriate salt solution on one side together with a reference electrode, usually Ag-AgCl, which is also sealed into the compartment containing tile salt solution. For other ions, the availability of suitable electrodes is quite restricted. The use of electrodes to measure the binding of small ions with proteins is based on the ideas that single ion activities can be measured with specific electrodes and that a decrease in activity of an ion in a protein solution is caused by an interaction (binding) of the ion with the protein.