TEMPO-oxidized cotton as a substrate for trypsin immobilization: impact of functional groups on proteolytic activity and stability

Cotton fibers containing different amounts of aldehyde and carboxyl groups were prepared by varying TEMPO oxidation conditions and then employed as carriers for trypsin immobilization. Depending on the functional group type present in the oxidized fiber, trypsin was immobilized through the ionic interaction or together with the Schiff’s base formation. The TEMPO oxidation caused changes in the chemical and physical properties of the modified cotton, which were evaluated by determining the aldehyde and carboxyl group content, sorption and electrokinetic properties, and surface morphology of fibers. The trypsin activity was assayed with N-α-benzoyl-dl-arginine p-nitroanilide hydrochloride, and the protein content was determined by the Bradford method. The impact of oxidized fiber functional groups on the amount, activity and stability of the immobilized trypsin was investigated. The cotton fibers oxidized under the most severe conditions (4.84 mmol/g NaClO, 180 min) and having the highest functional groups content (0.79 mmol/g) exhibited the maximum amount of immobilized trypsin of about 6.5 mg/g. However, the immobilized activity and the stability were much higher for the fibers containing both carboxyl and aldehyde groups compared to the corresponding fibers containing only carboxyl groups.