The effect of gel composition on the adsorption of invertase on poly(acrylamide/maleic acid) hydrogels

The effects of external stimuli such as pH of solution, temperature, substrate concentration of solution and storage stability on the invertase adsorption capacity of poly(acrylamide/maleic acid) [P(AAm/MA)] hydrogels, synthesized by gamma irradiation of ternary mixtures of AAm/MA/Water, were investigated. The adsorption capacities of the hydrogels were found to increase from 4.0 to 13.3 mg invertase/g dry gel with increasing amount of MA in the gel system, while P(AAm) gel adsorbed only 3.1 mg invertase/g dry gel. Kinetic parameters were calculated as 20.6 mM for Km and 6.44×10−5 mol/dm3 min for Vmax for free enzyme and in the range of 23.6–57.7 mM for Km and 8.62×10−5–1.05×10−4 mol/dm3 min for Vmax, depending on the amount of MA in the hydrogel. Enzyme activities were found to increase from 50.0 to 74.0% with increasing amount of MA in the gel system and retained their activities for one month storage. The enzyme activities, after storage at 4°C for one month, were found to be 21.0 and 50.0–74.0% of the initial activity values for free and adsorbed enzyme, respectively. The optimal pH values for free and adsorbed enzymes were determined as 4.56 and 4.56–5.00. The optimum temperature for free and adsorbed enzymes was 55°C. Adsorption studies show that, not only gel composition but also the stimuli, temperature and pH of the solution, play important roles on the invertase adsorption capacity of poly(AAm/MA) hydrogels.