Immobilization of papain by carboxyl-modified SBA-15: Rechecking the carboxyl after excluding the contribution of H2SO4 treatment

Carboxyl-modified mesoporous materials have been demonstrated as efficient carriers for immobilizing enzymes. However, little attention has been paid to the effect of H2SO4 treatment, a key in the synthesis of carboxyl-modified carriers, on the immobilization. To examine the H2SO4 treatment’s influence, we contrasted the ability of immobilizing papain between SBA-15 and the one after H2SO4 treatment (H2SO4-treated SBA-15). Meanwhile, the contribution of the as-synthesized carboxyl to the immobilization was also rechecked by comparing carboxyl-modified SBA-15 (COOH-SBA-15) and H2SO4-treated SBA-15. In relation to the experiments, the H2SO4 treatment increases the immobilizing ability of SBA-15, especially when the immobilization performs near the pI of papain. Moreover, the as-synthesized carboxyl facilitates the immobilization by means of strengthening the hydrophobic dehydration at the interface, instead of merely through electrostatic forces. Additionally, the carboxyl makes a large contribution to inducing the favorable conformation change of papain, improving the specific activity, catalytic efficiency, and binding affinity of the immobilized enzyme when combined with the substrate.

The carboxyl facilitates the immobilization of papain by means of strengthening the hydrophobic dehydration at the interface, instead of merely through electrostatic forces. Moreover, the carboxyl makes a large contribution to inducing the favorable conformation change of papain, improving the specific activity, catalytic efficiency, and binding affinity of the immobilized enzyme when combined with the substrate.Figure optionsDownload as PowerPoint slideHighlights
► The H2SO4 treatment increased the immobilization ability of SBA-15.
► Carboxyl assisted to the immobilization through enhancing the hydrophobic dehydration.
► Carboxyl had a contribution on inducing the favorable conformation change of papain.
► Papain/COOH-SBA-15 has higher activity and catalytic efficiency than the free one.
► Papain/COOH-SBA-15 has higher binding affinity with the substrate than the free one.