Matrix molecular weight cut-off for encapsulation of carbonic anhydrase in polyelectrolyte beads

The enzyme bovine carbonic anhydrase (BCA) has been immobilized in the chitosan-alginate system for the first time, to catalyze the conversion of CO2 to HCO3-. Chitosan-coated alginate beads are a biodegradable and environmentally benign matrix, chosen for application of the enzyme in a novel biomimetic CO2 sequestration system. The feasibility of the system and immobilization of the enzyme were demonstrated in our earlier studies. Optimization of the matrix to improve the retention time of the enzyme in an encapsulated form is the subject of the present study. The improvement in the molecular weight cut-off of the beads was accomplished by adjusting the cross-linking conditions, coating composition, and molecular weight of the system. The quantity of enzyme released from the system was measured by a Bio-Rad protein assay. Poly-L-lysine was also used as a coating reagent for comparison purposes. The presence of a coating on the alginate beads was verified by Kjeldahl analyses. The difference in the microstructures of alginate and chitosan/alginate beads was demonstrated by SEM studies. Mineralization of the chitosan/alginate matrix in the presence of CaCO3 was also studied by FT-IR, to assess the possibility of using the beads continuously in a bioreactor.