The surface activity of α-lactalbumin, β-lactoglobulin, and bovine serum albumin: II. Some molecular influences on adsorption to hydrophilic and hydrophobic silicon surfaces

Abstract

The thermal transitions experienced by α-lactalbumin (α-Lac), β-lactoglobulin (β-Lg), and bovine serum albumin (BSA) during a temperature ramp from 15 to 160°C were evaluated with differential scanning calorimetry. Adsorption isotherms were then constructed for each protein on hydrophilic and hydrophobic silicon surfaces at 2, 27, and 52°C. α-Lac exhibited a more or less steady increase in adsorption with temperature for each surface, with the increase in adsorbed mass beyond 27°C being consistent with an α-Lac transition occurring to facilitate favorable noncovalent contacts with the surface. Isotherms constructed at 27 and 52°C were similar for both β-Lg and BSA, which do not undergo a thermally induced transition until onset temperatures of about 64.0 and 54.4°C are reached, respectively. For each protein, adsorption was depressed at 2°C, consistent with decreasing stabilization by hydrophobic interactions and strengthening of hydrogen bonds occurring in the cold. Although adsorbed mass was observed to correlate reasonably well with molecular size at each temperature, the isotherm data are thought to provide only an indication of temperature and surface hydrophobic influences on relative amounts of single-component adsorption and not relative adsorption affinities; i.e., molecular size effects are simply incidental, and proteins with low stability and/or high flexibility are preferentially adsorbed.