Activity and structural stability of adsorbed enzymes

Abstract

A proteolytic enzyme, α-chymotrypsin, and a lipolytic enzyme, cutinase, were adsorbed from aqueous solution onto sorbent surfaces of varying hydrophobicity and morphology. With both enzymes the affinity of adsorption is larger for the hydrophobic surface. Water-soluble, flexible oligomers attached at the sorbent surface cause a reduction of the protein adsorption affinity. Circular Dichroism (CD) spectroscopy as well as Differential Scanning Calorimetry (DSC) indicate severe structural perturbations in the enzymes resulting from adsorption. The degree of structural perturbation, that is the fraction of the enzyme molecules that is perturbed by adsorption, decreases with decreasing hydrophobicity of the sorbent surface, with increasing degree of coverage of that surface by the enzyme, and with the presence of water-soluble oligomers at the sorbent surface. The specific activities of the enzymes are reduced upon adsorption, more or less following the extent of structural perturbation. When the enzyme is adsorbed its specific activity is much less sensitive to temperature variation.