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, cutinase, were adsorbed from aqueous solutions on solid surfaces with different hydrophobicities and morphologies. With both enzymes the affinity of adsorption is larger for the more hydrophobic surface. Water-soluble, flexible oligomers grafted on the sorbent surface cause a decrease in enzyme adsorption. CD spectroscopy and differential scanning calorimetry (DSC) indicate severe structural perturbations in the enzymes resulting from adsorption. The CD spectra reflect an average of the structure of the whole protein population. The DSC data allow additional conclusions to be drawn on the heterogeneity in the conformational states of the adsorbed enzymes. The degree of structural perturbation, that is the fraction of the adsorbed molecules of which the structure is perturbed, is lower at a surface that (1) is less hydrophobic, (2) contains water-soluble flexible oligomers and (3) is more covered by the protein. The specific activities of the enzymes are decreased on adsorption, more or less following the extent of structural perturbation. Unlike in solution, in the adsorbed state the heat-induced inactivation process is not identical with the heat-induced unfolding process. Furthermore, when the enzymes are adsorbed their specific activities are much less sensitive to temperature variation.