Encapsulation of urease in alginate beads and protection from alpha-chymotrypsin with chitosan membranes

Urease was encapsulated in alginate beads coated with chitosan, poly-L-lysi ne or poly(methylene co-guanidine) membrane to exclude a-chymotrypsin and o ther proteases. Urease in uncoated alginate. was highly susceptible to 21.6 kDa alpha -chymotrypsin, with 98% of the activity lost within 10 min expos ure. Chitosan and poly-L-lysine membrane coating provided 50 and 12% activi ty retention respectively after exposure, while poly(methylene co-guanidine ) membrane both inactivated urease and failed to provide protection from pr otease hydrolysis. Lyophilization of the beads caused shrinkage, and rehydr ated beads did not swell to their original diameter, effectively reducing p ermeability. This was evident through a large improvement in protease exclu sion for both chitosan-coated (89% activity retention) and uncoated (71%) b eads. Results with trypsin were similar to that observed with alpha -chymot rypsin, likely due to similarity in molecular weight. A higher level of exc lusion and urease protection within chitosan coated alginate beads was obse rved with higher molecular weight proteinase K. (C) 2001 Elsevier Science I nc. All rights reserved.