Immobilization of invertase enzyme on poly (vinylpyrrolidone-co-butylacrylate-co-n-hydroxymethyl acrylamide) terpolymer

In this study, invertase enzyme was immobilized on to Poly(VP-co-BAc-co-NHMAAm) by entrapment and covalent binding methods. Optimum temperature and pH values, reusability, storage life and kinetic parameters of both the free and immobilized enzyme have been investigated. Optimum temperature was found to be 50-55ºC for free enzyme, 70ºC for enzyme immobilized by entrapment method and 80ºC for enzyme immobilized by covalent binding method. It has also been found that the immobilization process increases the thermal stability of the enzyme. It was found that the optimum pH value was the same for the free enzyme and the enzyme immobilized by entrapment method, and this value was found to be as pH = 5. In the covalent binding method, this value was found to be as pH = 7. It has been found that the enzyme immobilized by both methods provides a larger pH working range than the free enzyme. The free and immobilized enzymes were analyzed for their reusability at different periods. It was observed that the immobilized enzyme still had an activity after reusing 60 times. The enzyme immobilized covalently retained 85% of its original activity and the enzyme immobilized by entrapment method retained 90% of its original activity after storage of 7 months. The free enzyme had lost all of its original activity in this period. Km and Vmax values were determined for both the free enzyme and the enzyme immobilized by both methods. It has been observed that the immobilized enzymes had lower Km values than free form. Key words: Vinyl pyrrolidone, Butyl acrylate, N-hydroximethyl acrylamide terpolymer, entrapment, covalent binding, invertase, enzyme immobilization.