It was found that the adsorption was completely reproducible with tamination in food processing, and, in the case of an implant, respect to lysozyme concentration, but it was irreversible. The lead to a complete rejection of the implant (1).
effect of ionic strength on the adsorption of lysozyme was exam-Much effort has recently been made to investigate the ined at pH 7 and at a bulk lysozyme concentration of 0.03 g dm 03 .
interaction of proteins with different solid substrates. Al-The adsorbed layer was not affected by changes in ionic strength when the total ionic strength was below 0.05 M, but above this though many studies have shown that the amount of protein concentration addition of NaCl gradually reduced the amount of adsorbed on a solid substrate is strongly influenced by the lysozyme adsorbed. Complete removal of adsorbed lysozyme was interaction between the surface and the protein, the level of achieved when the total ionic strength was above 0.5 M. The effect adsorption can also be easily altered by a shift in the balance of solution pH on the amount of lysozyme adsorbed was characterof the interactions involved, i.e., electrostatic forces, van der ized by varying the pH in cycles at fixed lysozyme concentrations. Waals forces, conformational entropy changes, and hy-Adsorption was found to be completely reversible with respect to drophobic interactions (2). Strong interaction between pro-pH over a wide protein concentration range. The level of surface tein molecules and the solid surface often leads to irreversexcess was dominated by the electrostatic repulsion between lysoible adsorption, which in many cases is marked by the loss zyme molecules within the adsorbed layers, rather than the atof secondary or tertiary structure and the eventual denaturtraction between the surface and lysozyme. The lysozyme layer ation of the protein. The nature of the solid surface, including structure along the surface normal was characterized by varying the isotopic composition of the water. At pH 7 a monolayer 30 { its hydrophobicity, charge type, and density, has a dominant 2 A ˚thick was formed when the lysozyme concentration was below effect on the structure and conformation of the resultant 0.03 g dm 03 , indicating that the lysozyme was adsorbed with its protein layers, but the effect of the surface is often complilong axis parallel to the surface (sideways-on). At higher concencated by the charge, stability and surface hydrophobicity of trations the thickness of the layer changed to 60 { 2 A ˚, suggesting the protein molecules themselves. Haynes and Norde (3) the formation of a bilayer of lysozyme molecules in the sidewayshave recently studied the adsorption of lysozyme and bovine on configuration. When the lysozyme concentration is above 1 g milk a-lactalbumin, both of which are globular molecules dm 03 the surface excess within the inner layer is sufficiently high of similar size, on surfaces with different charge density and that repulsion within the adsorbed layer becomes significant and hydrophobicity. They found that on adsorption to a hydrothe molecules start to tilt towards longways-on adsorption. At pH philic surface lysozyme retained most of its tertiary structure 4, the electrostatic repulsion between the adsorbed molecules is while a-lactalbumin lost almost all of its native conformastronger than at pH 7, resulting in a lower surface excess and a tilting away from the sideways-on configuration at lower surface tion. The same authors also found that adsorption onto a concentration. ᭧ 1998 Academic Press hydrophobic polystyrene surface induced the exposure of Key Words: protein adsorption; neutron reflection; lysozyme adthe hydrophobic fragments of both proteins, leading to their sorption; solid-water interface; protein folding. denaturation. Although most studies suggest that adsorption onto hydrophobic surfaces causes very severe structure deformation, Maste et al. (4) and Zoungrana et al. (5) have