Using a stirred cell to evaluate structural changes in proteins adsorbed on particles

A stirred cell technique was used to evaluate structural changes in proteins adsorbed on particles. Stirred cell geometry was used to obtain a series of breakthrough curves, which is the change in the concentration of the adsorbate in the effluent as a function of effluent volume. The breakthrough curves can be asymmetric, which arises from the combination of factors related to the efficiency of the sorption process. The substrate consisted of a 1.5 volume percent suspension of nonporous latex particles mixed at high rotation speed. The adsorption of proteins on to hydrophobic surfaces, such as polystyrenes (PS) was modeled as a two-step process, reversible adsorption until the surface was fully covered with protein molecules, followed by irreversible structural changes in the adlayer. The pH values were chosen to match the isoelectric point of each protein, to minimize electrostatic interactions between the proteins and the PS latex, and to simultaneously maximize the amount of protein adsorbing through hydrophobic interactions. The results show that structural changes can be assessed as a function of protein concentration, and may include orientational and/or conformational changes, association and dissociation.