Surfactant-selective electrode study of bile salt—protein binding

Abstract

An electrode selective to bile salt anions, has been evaluated for use in bile salt solutions and solutions containing bile salt anions and a protein. The electrode potential values obtained are a direct function of the activities of the corresponding bile salt anions. The electrode potential, follows Nernstian behavior in the premicellar region of bile salt solutions. A minimum is observed in the Nernst plot corresponding to the critical micelle concentration. Results obtained using these electrodes in solutions containing protein and bile salt have been used to construct Scatchard plots for the bile anion-protein binding. The treatment of the data with non-linear least-squares fit gave estimates of the binding constants and the number of binding sites which are comparable to previous results obtained from equilibrium dialysis measurements. Five bile salts studied bound in the following relative order: sodium deoxycholate ∼- sodium chenodeoxycholate > sodium ursodeoxycholate > sodium cholate > sodium dehydrocholate. Binding studies were also carried out as a function of temperature which enabled the estimation of thermodynamic functions of binding. ΔH° of binding is positive suggesting that these biological detergents bind to hydrophobic sites on serum albumin.