KINETICS OF LYSOZYME ADSORPTION AT THE AIR-BUFFER INTERFACE

The adsorption of lysozyme at the air-buffer interface has been monito red previously by a radiotracer method. A major experimental feature o f these studies is that the amount of protein adsorbed is a significan t fraction of the protein in the bulk at the beginning of the adsorpti on process. In the present study, several kinetic models of adsorption are derived which take into account the bulk protein concentration an d a possible attraction of the protein in solution by the protein mole cules forming the interfacial adsorption layer. Moreover, the data are analyzed assuming either an exponential regime (the rate of adsorptio n is controlled by the distance from equilibrium) or a diffusive regim e (the rate of adsorption is controlled by the diffusion of protein mo lecules in the solution). The full model (depletion of protein from th e bulk and attraction by the previously adsorbed molecules) leads to a n expression for the rate of adsorption of the third degree. Only the third degree gives a good fit to the experimental data where two kinet ic phases are obvious. However, the accuracy of the data does not allo w us to determine whether the adsorption regimes are diffusive or expo nential. It may be concluded that the adsorption of lysozyme at the ai r-buffer interface is very probably a 'cooperative' process.