ADSORPTION OF BETA-LACTOGLOBULIN-A AND BETA-LACTOGLOBULIN-B IN RELATION TO SELF-ASSOCIATION - EFFECT OF CONCENTRATION AND PH

Adsorption of beta-lactoglobulin A and B onto hydrophilic and methylat ed silica surfaces was studied by in situ ellipsometry. The adsorbed a mount versus time was measured during adsorption for 1 h, followed by rinsing (5 min at 20 mL/min) and another 25 min of desorption. The eff ect of protein concentration (0.3 x 10(-4) to 3 mg/mL) on the plateau values of the adsorbed amount as well as on the adsorption kinetics co uld be related to the degree of self-association in solution. The adso rption isotherms of beta-lactoglobulin A and B, in 0.01 M phosphate bu ffer (I = 0.017), pH 7.0, at 25 degrees C exhibit a two-mode binding b ehavior and were found to be shifted in concentration by a factor corr esponding to the difference in dimer-monomer dissociation constants. P referential adsorption of dimers was indicated from the adsorption kin etics. The influence of pH on the adsorption to methylated silica of t he proteins at a concentration of 0.3 mg/mL in 0.01 M NaCl was related to the variation in self-association within the pH interval (2.0-7.0) .