A Kinetic Study on the Adsorption of Compact, Water-soluble Proteins onto Aqueous Surfaces

摘要

Two compact sized globular proteins, モ-lactoglobulin and メ-lactalbumin were kinetically characterized at the aqueous solution surface with the measurement of surface pressure (ヰ) and surface concentration (ッ) via a radiotracer method. The adsorption kinetics was of diffusion control at early times, the rates of increase of ヰand ッ being lower at longer times due to growing energy barrier. At low concentrations, an apparent time lag was observed in the evolution of ヰ for モ-lactoglobulin but not for メ-lactalbumin which was shown to be due to the non-linear nature of the p- G relationship for the former. The area per molecule of an adsorbed モ-lactoglobulin during adsorption was smaller than that for spread monolayer since モ-lactoglobulin was not fully unfolded during the adsorption. For メ-lactalbumin, however, no such difference in the molecular areas for adsorbed and spread monolayer was observed indicating thereby that メ-lactalbumin unfolded much more rapidly (has looser tertiary structure) than モ-lactoglobulin. Surface excess concentrations of メ-lactalbumin was found to evolve in two steps possibly due to the change in the orientation of the adsorbed protein from a side-on to an end-on orientation.