Binding studies using ion-selective electrodes. Examination of the picrate-albumin interaction as a model system.

We are studying the binding of ligands to macromolecules by using ligand ion selective electrodes as transducers. The picrate-bovine albumin interaction is examined in detail as a model system. A picrate ion selective electrode is used to monitor the free picrate concentration directly in the presence of albumin and bound ligand. The binding parameters are estimated and the effect of protein concentration, ionic strength, pH, and temperature is studied. The experimental data are interpreted with a specially designed computer program that performs nonlinear least-squares fitting of the generalized Scatchard model with an infinite number of classes of binding sites directly to the raw potentiometric data. The binding parameters (binding constant and maximum number of ligands that can be bound), the nonspecific binding as well as their standard deviations are estimated by this program. The principles described can be used for the potentiometric study of any ligand-binder interaction.