STRUCTURE OF ADSORBED AND DESORBED PROTEINS

Two proteins, bovine serum albumin (BSA) and hen's egg lysozyme (LSZ), having different structural stabilities, were adsorbed from aqueous solution onto finely dispersed silica particles. The structural rearrangements in the protein molecules upon adsorption and subsequent displacement by morpholine were probed by determining the alpha-helix content from the circular dichroism of the proteins. With both proteins the alpha-helix content decreases upon adsorption, but this effect diminishes with increasing coverage of the sorbent surface by the protein. At plateau adsorption the reduction in helix in LSZ is insignificant, whereas in BSA it is still considerable. With LSZ it is observed that the magnitude of structural rearrangements is increased with increasing charge contrast between the protein and the sorbent. Upon displacement, the amount of helical structure in LSZ is not different from that in the adsorbed state (under plateau conditions) and, hence, not different from that in the native molecule in solution, With BSA, displacement leads to recovery of the helix content. but not to the level that exists in the native molecule.