A monoaminated dextran derivative wits attached to trypsin via a carbodiimide-catalyzed reaction. The modified enzyme contained 3 mol of polysaccharide per mol of protein, and retained about 93% and 85% of the native esterolytic and proteolytic activity, respectively. The thermostability was enhanced from 49.7 to 67.4 degrees C for modified trypsin. The activation free energy of thermal inactivation at 55 degrees C was increased by 7.2 kJ/mol for the protease after modification with the polymer. The improved conformational stability of trypsin after glycosidation with dextran was confirmed by fluorescence spectroscopy. The glycosidated protease retained 70% of its initial activity after 3 It incubation at pH 9.0. (c) 2005 Elsevier Ltd. All rights reserved.