SURFACE-INDUCED CHANGES IN THE STRUCTURE AND ACTIVITY OF ENZYMES PHYSICALLY IMMOBILIZED AT SOLID LIQUID INTERFACES/

A proteolytic enzyme, alpha-chymotrypsin, and a lipolytic enzyme, cuti nase, were adsorbed from aqueous solutions on solid surfaces with diff erent hydrophobicities and morphologies, With both enzymes the affinit y of adsorption is larger for the more hydrophobic surface. Water-solu ble, flexible oligomers grafted on the sorbent surface cause a decreas e in enzyme adsorption. CD spectroscopy and differential scanning calo rimetry (DSC) indicate severe structural perturbations in the enzymes resulting from adsorption. The CD spectra reflect an average of the st ructure of the whole protein population, The DSC data allow additional conclusions to be drawn on the heterogeneity in the conformational st ates of the adsorbed enzymes. The degree of structural perturbation, t hat is the fraction of the adsorbed molecules of which the structure i s perturbed, is lower at a surface that (1) is less hydrophobic, (2) c ontains water-soluble flexible oligomers and (3) is more covered by th e protein. The specific activities of the enzymes are decreased on ads orption, more or less following the extent of structural perturbation. Unlike in solution, in the adsorbed state the heat-induced inactivati on process is not identical with the heat-induced unfolding process. F urthermore, when the enzymes are adsorbed their specific activities ar e much less sensitive to temperature variation.