The effect of external stimuli on the invertase adsorption capacity of poly(N-vinyl-2-pyrrolidone-co-itaconic acid) hydrogels

Polyelectrolyte Poly(N-vinyl-2-pyrrolidone-co-itaconic acid) hydrogels (P(V P/IA)) with varying compositions were prepared from ternary VP/IA/water mix tures. The effect of external stimuli such as pH of the solution, temperatu re, substrate concentration of solution, and storage stability on the inver tase adsorption capacity of P(VP/IA) hydrogels was investigated. The adsorp tion capacity of the hydrogels was found to increase from 4.4 to 18.4 mg in vertase/g dry gel with increasing amount of IA in the gel system, while P(V P) gel adsorbed only 3.1 mg invertase/g dry gel. Kinetic parameters were ca lculated as Michaelis-Menten constant K-m = 20.6 mmoI L-1 and maximum veloc ity V-max = 6.44 x 10(-5) mol dm(-3) min(-1) for free enzyme and in the ran ge of K-m = 26.4 -41.1 mmol L-1 and V-max = 6.35.10(-5)-6.66.10(-5) mol dm( -3) min(-1), depending on the amount of IA in the hydrogel. Enzyme activiti es were found to increase from 59.0% to 72.0% with increasing amount of IA in the gel system and retained their activities for one month storage. The enzyme activities, after storage for one month at 4 degrees C, were found t o be 21.0% and 59.0-74.0% of the initial activity values for free and adsor bed enzyme, respectively The optimal pH values for free and adsorbed enzyme s were determined as 4.56 and 5.00, respectively. The optimum temperature f or free and adsorbed enzymes was 55 degrees C. Adsorption studies have show n that not only the gel composition but also the stimuli, temperature and p H of the solution play an important role on the invertase adsorption capaci ty of poly(VP/IA) hydrogels.