KINETICS OF ADSORPTION OF LYSOZYME AND BOVINE SERUM-ALBUMIN AT THE AIR-WATER-INTERFACE FROM A BINARY MIXTURE

The kinetics of adsorption of lysozyme and bovine serum albumin (BSA) at the air-water interface from binary bulk mixtures have been studied . An increase in BSA concentration in bulk phase caused a decrease in the extent of adsorption of lysozyme and an exponential decrease in it s apparent diffusion coefficient; the lag time for its adsorption, how ever, decreased progressively with increasing bulk concentration of BS A. The ratio of BSA to lysozyme in the mixed monolayer increased with increasing ratio of BSA to lysozyme in the bulk phase. However, the un it cell dimensions occupied by BSA and lysozyme in the mixed monolayer were the same as those in single-component monolayers, suggesting tha t both BSA and lysozyme adsorbed independently, and the thermodynamic state of one protein was not modified by the other protein at the inte rface. Analysis of variations in interfacial composition of mixed mono layers formed at various bulk concentration ratios of the proteins ind icated that adsorption of these proteins from the binary bulk phase di d not follow a Langmuir-type competitive adsorption mechanism. Sequent ial adsorption experiments showed that although bulk phase BSA abruptl y stopped adsorption of lysozyme, it could not displace lysozyme alrea dy adsorbed at the interface. In contrast, bulk phase lysozyme could n either stop adsorption of BSA nor displace adsorbed BSA. Critical anal ysis of these results indicated that adsorption of BSA and lysozyme fr om binary mixtures followed a kinetically controlled, noncompetitive a dsorption mechanism. The interfacial composition of the mixed protein layer was primarily, if not solely, determined by the rate of arrival of each protein at the interface and unoccupied unit cells available a t the interface at the time of arrival. (C) 1995 Academic Press, Inc.