Binary protein adsorption on gel-composite ion-exchange media

Abstract

The adsorption kinetics of mixtures of lysozyme and cytochrome-C on S-HyperD-M, a cation exchanger composed of a rigid macroporous silica matrix whose pores are filled with a functionalized polyacrylamide gel, was characterized. Single-component isotherms were found to follow approximately the steric mass-action law of Brooks and Cramer, and an extension of this model to a binary system was consistent with two-component uptake equilibrium results. Transient adsorption experiments were done to investigate the kinetics of sequential and simultaneous adsorption of the two proteins. At low protein concentrations, adsorption is essentially noncompetitive, and mass transfer is controlled by the external film resistance. At higher concentrations, equilibrium becomes competitive and coupling of the intraparticle diffusion fluxes occurs. A model based on a Maxwell-Stefan approach, where the driving force for diffusion is expressed in terms of the chemical potential gradient, was in approximate agreement with the experimental results.