ADSORPTION OF MODEL PROTEINS WITH WIDE VARIATION IN MOLECULAR-PROPERTIES ON COLLOIDAL PARTICLES

To elucidate some general principles of protein adsorption, the adsorption isotherms of ribonuclease A (RNase A), cytochrome c, lysozyme, α-lactalbumin, ovalbumin, and bovine serum albumin (BSA) on colloidal particles of polystyrene, styrene/2-hydroxyethyl methacrylate, and silica were measured as a function of pH and ionic strength. These proteins were different, especially with respect to molecular flexibility. All adsorption isotherms showed plateaus. While affinities of all proteins for hydrophilic particles decreased significantly with increasing pH, those for hydrophobic particles were high irrespective of pH. At an ionic strength of 0.01, the pH dependence of the plateau adsorption of small proteins (RNase A, cytochrome c, lysozyme, and α-lactalbumin) was affected by the surface properties of the particles, while that of large proteins (ovalbumin and BSA) showed the maximum at around their isoelectric points irrespective of the type of particles. On the other hand, the pH dependence of the plateau adsorption was related to the surface properties at an ionic strength of 0.1 irrespective of the type of protein. The above dependence of protein adsorption on properties of solid surfaces and adsorption conditions did not vary with the molecular flexibility of the proteins, although the structural changes in the flexible protein molecules upon adsorption promoted adsorption. Therefore, both the protein-surface interactions, such as hydrophobic and electrostatic ones, and the lateral interaction between adsorbed molecules are dominant factors that control protein adsorption on these particles. © 1992.