A spectroscopic study on the absorption of carbonic anhydrase onto the nanoporous silica nanoparticle

Herein, KIT-6 nanoporous silica nanoparticles were used as a solid support for immobilization of bovine carbonic anhydrase, isoform II (BCA II). The zeta potential study revealed that KIT-6 and BCA II provided negative (−13.58 ± 1.95 mV) and positive (4.23 ± 0.72 mV) charge distribution, respectively. Dynamic light scattering (DLS) analysis also showed that the hydrodynamic radius of KIT-6 is less than 100 nm. In addition, the structural studies of free and immobilized BCA II against urea-induced denaturation were investigated by circular dichroism (CD) and fluorescence spectroscopy. CD studies showed that the absorbed BCA II, in comparison with the free enzyme, demonstrated higher stability against rising urea concentration. Fluorescence spectroscopy showed lower values of Stern- Volmer constant (KSV) for immobilized BCA II relative to free enzyme, reflecting the relative enzyme stability of BCA II after immobilization. Melting temperature (Tm) measurement of free and immobilized BCA II showed that immobilized enzyme had a more stable structure (Tm = 71.9 °C) relative to the free counterpart (Tm = 64.7 °C). In addition, the immobilized BCA II showed pronounced stability against pH and thermal deactivation. This study may provide new and complementary details regarding the design and development of enzymes in industrial applications.