STRUCTURE, STABILITY, AND ACTIVITY OF ADSORBED ENZYMES

A proteolytic enzyme, alpha-chymotrypsin, and a lipolytic enzyme, cuti nase, were adsorbed from aqueous solution onto a hydrophobic Teflon su rface and a hydrophilic silica surface. We investigated the influence of adsorption on the structure, the structure thermal stability and th e activity of these enzymes. Probing the protein structure by circular dichroism spectroscopy indicates that Teflon promotes the formation o f helical structure in alpha-chymotrypsin, but the reverse effect is f ound with cutinase. The perturbed protein structures on Teflon are rem arkably stable, showing no heat-induced structural transitions up to 1 00 degrees C, as monitored by differential scanning calorimetry. Conta ct with the hydrophilic silica surface leads to a loss in the helix co ntent of both proteins. Differential scanning calorimetry points to a heterogeneous population of adsorbed protein molecules with respect to their conformational states. The fraction of the native-like conforma tion in the adsorbed layer increases with increasing coverage of the s ilica surface by the proteins. The specific enzymatic activity in the adsorbed state qualitatively correlates with the fraction of proteins in the nativelike conformation. (C) 1997 Academic Press.