Bovine pancreatic alpha-chymotrypsin was covalently modified with the O-carboxymethyl poly-beta-cyclodextrin (M = 1.3 x 10(4) 40% COOH groups) using a water-soluble carbodiimide as a coupling agent. The conjugate prepared by this procedure retained high proteolytic and esterolytic activity and contained about 74% carbohydrate by weight of transformed protein. The optimum temperature for alpha-chymotrypsin was increased by 5 degreesC after this transformation. The thermostability of the polymer-enzyme adduct was also increased by 5 degreesC. The conjugate prepared was also more resistant to thermal inactivation at different temperatures, ranging from 45 to 55 degreesC. Additionally, the modified enzyme was 11-fold more stable at pH 9.0. The direct influence of supramolecular interactions between the hydrophobic amino acid residues located at the surface of the protease and the attached polycyclodextrin moieties on alpha-chymotrypsin stabilization was demonstrated. (C) 2003 Elsevier Ltd. All rights reserved.