The proteases viz. a-chymotrypsin, trypsin and papain were immobilized on tri(4-formyl phenoxy) cyanurate to form Schiffs base. The native and immobilized proteases were used for catalyzing the hydrolysis of proteins in an aqueous medium. Immobilized a-chymotrypsin exhibited shift in optimal pH from 8.5 to 9.0, while both trypsin and papain exhibits shift in optimal pH from 8.0 to 8.5. The shift in optimal temperature from 40 to 50 degrees C was recorded for alpha-chymotrypsin and trypsin, while papain shifted the optimal temperature from 50 to 60 degrees C. The immobilized protease revealed 15-20% increased in thermal stability and retained 70-80% of its initial activity after 8 cycles. The optimum in vitro proteolytic activity on animal intestine was recorded for papain in comparison with trypsin and a-chymotrypsin. These results support the diet-related plasticity of proteases. (c) 2006 Elsevier Inc. All rights reserved.