Invertase immobilized on spacer-arm attached poly(hydroxyethyl methacrylate) membrane: Preparation and properties

Microporous poly(2-hydroxyethyl methacrylate) (pHEMA) membrane was prepared by UV-initiated photopolymerization. The spacer arm (i.e., hexamethylene d iamine) was attached covalently and then invertase was immobilized by the c ondensation reaction of the amino groups of the spacer arm with carboxyl gr oups of the enzyme in the presence of carbodiimides. The values of the Mich ael's constant K-m of invertase were significantly larger (ca. 2.5 times) u pon immobilization, indicating decreased affinity by the enzyme for its sub strate, whereas V-max was smaller for the immobilized invertase. Immobiliza tion improved the pH stability of the enzyme as well as its temperature sta bility. Thermal stability was found to increase with immobilization and at 70 degrees C the half times for the activity decay were 12 min for the free enzyme and 41 min for the immobilized enzyme. The immobilized enzyme activ ity was found to be quite stable in repeated experiments. (C) 2000 John Wil ey & Sons, Inc.