Adsorption of beta-lactoglobulin A and B: Effects of ionic strength and phosphate ions

The effect of ionic strength in phosphate buffer and in pure NaCl solution on the adsorption onto hydrophilic and methylated silica surfaces for beta-lactoglobulin A and B was studied by in-situ ellipsometry. On hydrophilic silica, increased adsorbed amounts as well as faster kinetics were found for beta-lactoglobulin (beta-1g) B with increasing ionic strength in pure NaCl solution. The adsorbed plateau values obtained for the A variant were seen to be unaffected by ionic strength both in pure NaCl solution (on methylated silica) and in the presence of phosphate (on methylated as well as on hydrophilic silica). A decrease in adsorbed amounts, for beta-1g B on the two types of surface and for a 1:1 mixture of the A and B variants on methylated silica in the presence of phosphate at high ionic strength (I=0.17) suggested a specific interaction with phosphate ions for the B variant. The interaction takes place only at higher ionic strength and probably gives rise to increased dissociation of the dimers. (C) 1997 Elsevier Science B.V.