SIMPLE-MODELS FOR ADSORPTION-KINETICS AND THEIR CORRELATION TO THE ADSORPTION OF BETA-LACTOGLOBULIN-A AND BETA-LACTOGLOBULIN-B

A description of general models for adsorption kinetics is given. Comb inations of the models are compared with adsorption data for the self- associating proteins P-lactoglobulin A and B, from Elofsson et al. (U. M. Elofsson, M. A. Paulsson, and T. Arnebrant, Langmuir, submitted). The adsorption onto methylated silica surfaces was measured by these a uthors by ellipsometry in phosphate buffer (0.01 M, pH 7.0) at five co ncentrations in the range 0.0003-3 mg/ml. Two models, which agree with the experimental data to a reasonable extent, are presented. These mo dels both contain exchange reactions between adsorbed monomers and dim ers from solution. Furthermore, they include three classes of adsorbed molecules, dimers, and two types of monomers. The monomer types diffe r in the rate with which they could be displaced by dimers from the so lution. The difference between the two models was in the description o f how the less easily displaced monomer form was obtained. In one mode l they were obtained by an exchange reaction between monomers, depende nt on the surface coverage of dimers. In the other they were obtained by displacement of adsorbed monomers by dimers which dissociated upon adsorption. The models could be used to describe the adsorption kineti cs of both the A and B variants of P-lactoglobulin at five different c oncentrations. However, the rate constants differed with a factor of 7 .9 between the two proteins, which is of the same size as the differen ce in the monomer-dimer equilibrium constant. Other models tested, whi ch were found not to fit the data, include for example simple surface dimerization and pure competitive adsorption. (C) 1997 Academic Press.