A versatile approach
to entrap relatively small enzymes in hydrogels
allows their diverse biotechnological applications. In the present
work, bovine carbonic anhydrase (BCA) was efficiently entrapped in
calcium alginate beads with the help of liposomes. A mixture of sodium
alginate (3 wt %) and carbonic anhydrase–liposome conjugates
(BCALs) was dripped into a Tris-HCl buffer solution (pH = 7.5) containing
0.4 M CaCl2 to induce the gelation and curing of the dispersed
alginate-rich droplets. The entrapment efficiency of BCALs, which
was defined as the amount of catalysts entrapped in alginate beads
relative to that initially charged, was 98.7 ± 0.2% as determined
through quantifying BCALs in the filtrate being separated from the
beads. When free BCA was employed, on the other hand, a significantly
lower entrapment efficiency of 27.2 ± 4.1% was obtained because
free BCA could pass through alginate matrices. Because the volume
of a cured alginate bead (10 μL) entrapped with BCALs was about
2.5 times smaller than that of an original droplet, BCALs were densely
present in the beads to give the concentrations of lipids and BCA
of 4.6–8.3 mM and 1.1–1.8 mg/mL, respectively. Alginate
beads entrapped with BCALs were used to catalyze the hydrolysis of
1.0 mM p-nitrophenyl acetate (p-NA)
at pH = 7.5 using the wells of a microplate or 10 mL glass beakers
as batch reactors. Furthermore, the beads were confined in a column
for continuous-flow hydrolysis of 1.0 mM p-NA for
1 h at a mean residence time of 8.5 or 4.3 min. The results obtained
demonstrate that the conjugation of BCA to liposomes gave an opportunity
to achieve efficient and stable entrapment of BCA in alginate hydrogels
for applying to catalytic reactions in bioreactors.