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

Abstract

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 [1–3]. 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 crosslinking 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.

Keywords:

• Chitosan
• alginate
• carbonic anhydrase
• CO2 sequestration
• encapsulation
• mineralization.