THE BINDING OF ANIONS BY LYSOZYME, CALF THYMUS HISTONE SULPHATE, AND PROTAMINE SULPHATE

Abstract

The adsorption of a large series of anions by positively charged lysozyme, calf thymus histone sulphate, and protamine sulphate has been studied by dialysis equilibrium. One group of anions was not adsorbed by lysozyme while the adsorption isotherms for Orange I, Orange II, and 2, 4-dinitro-1-naphthol-7-sulphonic acid were S-shaped. These anomalous isotherms, which were also obtained with histone sulphate and protamine sulphate, have an appreciable temperature coefficient at intermediate dye concentrations. It is emphasized that this type of adsorption is inconsistent with the exclusively electrostatic view of protein binding of anions. It is also shown that −ΔF, −ΔH, and ΔS per mole of anion bound must pass through a maximum for intermediate free anion concentrations in such systems. The lack of binding of some anions and the anomalous isotherms for others is interpreted in terms of a solvation sheath about the charged protein. Their significance for the general process of binding of ions by proteins is discussed.