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, substr ate concentration of solution and storage stability on the invertase adsorp tion capacity of poly(acrylamide/maleic acid) [P(AAm/MA)] hydrogels, synthe sized by gamma irradiation of ternary mixtures of AAm/MA/Water, were invest igated. The adsorption capacities of the hydrogels were found to increase f rom 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. Kine tic parameters were calculated as 20.6 mM for K-m and 6.44x10(-5) mol/dm(3) min for V-max for free enzyme and in the range of 23.6-57.7 mM for K-m and 8.62x10(-5) -1.05x10(-4) mol/dm(3) min for V-max, depending on the amount of MA in the hydrogel. Enzyme activities were found to increase from 50.0 t o 74.0% with increasing amount of MA in the gel system and retained their a ctivities for one month storage. The enzyme activities, after storage at 4 degrees C for one month, were found to be 21.0 and 50.0-74.0% of the initia l activity values for free and adsorbed enzyme, respectively. The optimal p H values for free and adsorbed enzymes were determined as 4.56 and 4.56-5.0 0. The optimum temperature for free and adsorbed enzymes was 55 degrees 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. (C) 2000 Elsevier Science L td. All rights reserved.