The immobilization of trypsin, chymotrypsin and carboxypeptidase A using 4 and 10% glyoxyl-agarose beads at different times of incubation was investigated. Enzyme loadings of 30 mg/mL gel for trypsin and chymotrypsin, and 2 mg/mL gel for carboxypetidase A were used. Immobilization rates were very rapid in both supports and reactions were completed after I h of reaction. Final residual activities at these concentrations were around 60% for trypsin and chymotrypsin, and 50% for carboxypeptidase A. Comparison of the thermal stability of the soluble and immobilized enzymes revealed that immobilization by binding to 10% glyoxyl-agarose yielded the most stable enzymatic activities. Reaction with this support yielded immobilized trypsin, chymotrypsin, and carboxypeptidase A that were 4700, 10,000, and 1000 times more stable than the soluble enzymes, respectively. It was observed that the number of lysine residues that took part in the immobilization process was a consequence of the type of support and reaction time of the experimental conditions, and that the increasing of the thermal stability of the derivatives was correlated with a increasing number of lysines residues involved in a multipoint covalent attachment. (c) 2006 Elsevier Inc. All rights reserved.