Structure and activity of magnetic cross-linked enzyme aggregates of bovine carbonic anhydrase as promoters of enzymatic CO2 capture

CO2 absorption into aqueous solutions promoted by carbonic anhydrase (CA) is a potential post-combustion CO2 capture process. Carbonic anhydrase (EC 4.2.1.1) is an enzyme that catalyzes CO2 hydration with high turnover numbers. This work is aimed at developing CA-based biocatalysts applying the technique of magnetic Cross-Linked Enzyme Aggregates (CLEAs) to bovine carbonic anhydrase (bCA) and magnetic nanoparticles (NPs). The CLEAs were obtained by crosslinking the precipitated bCA/NPs aggregates with glutaraldehyde. Optimum conditions for the immobilization procedure were assessed in terms of type of precipitating agent, concentration of glutaraldehyde, crosslinking operating conditions, and concentration of magnetic NPs. The optimization was carried out with respect to the maximum immobilization yield and to the CLEA activity. The maximum immobilization yield was 84% and the maximum activity (1268 WAU/mgCLEA) was measured for CLEAs prepared with 100 mM glutaraldehyde at 4 °C, after 16 h crosslinking and 0.5 gNPs/gbCA. Morphological analysis of CLEAs prepared under different conditions was carried out by optical microscopy. Vigorous stirring during the precipitation step provided reduction of aggregates size that was slightly modified by magnetic field separation. Moreover, the morphological analysis shows evidence of some detrimental effects of high NPs concentration on CLEAs activity.