Poly(methylene co-guanidine) coated alginate as an encapsulation matrix for urease

Urease was encapsulated within alginate beads, coated with poly(methylene co-guanidine) membranes via polyelectrolyte complexation. Membrane thickness increased with reaction time to 53 mu m after 80 min, and to 59 mu m with an increase in co-guanidine concentration from 2.5 to 20 mg ml(-1). A 70% mass and 31% activity yield of urease resulted following encapsulation. Although co-guanidine strongly inhibited freely soluble urease (I-0.5 = 5.8 mu g ml(-1) co-guanidine), immobilization stabilized the enzyme against inactivation. Encapsulated activity declined as the polycation concentration used for membrane formation increased; however an activity loss of only 35% was observed when the co-guanidine concentration was as high as 5 mg ml(-1). Glucose protected against inactivation, with I-0.5 increasing to 28.5 mu g ml(-1) for the freely soluble enzyme. When the beads were coated with co-guanidine in the presence of glucose, encapsulated urease activity was fully retained. (C) 2000 Elsevier Science Ltd. All rights reserved.