Preparation and functional properties of trypsin modified by carboxymethylcellulose

Trypsin from bovine pancreas was modified by the polyaldehyde derivative of carboxymethylcellulose (CMC) via reductive alkylation with NaBH4. The modified enzyme contained 57% carbohydrate by weight, resulting from the modification of 52% of the amino groups of the protein. In comparison with the native protease, the modified trypsin retained 62% and 42% of the esterolytic and proteolytic activity, respectively. The value of Km for CMC–trypsin complex was 2.2 times lower than for the native enzyme. The thermostability and pH stability was improved for trypsin by this modification. The conjugate was also more resistant to the action of the anionic surfactant sodium dodecylsulphate and denaturing agents such as 8 M urea and 6 M guanidinium chloride. This modification also protected the enzyme against autolysis at alkaline pH and improved the stability of the enzyme in the presence of methanol.