Energetics of protein-interface interactions and its effect on protein adsorption

The kinetics of adsorption of several positively and negatively charged pro teins at the air/water and triolein/water interfaces have been studied. It is shown that adsorption of proteins at these interfaces is not simply diff usion-controlled but is strongly influenced by the energetics of interactio n of proteins with the interfaces. Generally, positively charged proteins e xperience an energy barrier for adsorption at the air-water interface and t herefore exhibit adsorption rates an order of magnitude slower than their r espective bulk diffusivities. In contrast, the negatively charged proteins exhibit an attraction toward the air/water interface and therefore their ad sorption rates are either slightly higher or 1.5-2 times lower than their b ulk diffusivities. At the triolein-water interface however, all proteins, e xcept phosvitin, adsorbed at rates 1-2 orders of magnitude faster than thei r bulk diffusivities. The differences between absorptivities of positively and negatively charged proteins at the air-water interface, and the differe nces between absorptivities of all proteins at the air/water and triolein/w ater interfaces can be explained convincingly in terms of the energetics of interaction of proteins with the interfaces.