Enzyme encapsulation in silica gel prepared by polylysine and its catalytic activity

摘要

Enzymes used in industrial applications are often immobilized onto different types of supports because they are sensitive to pH, temperature, and various other environmental conditions. However, many of the current immobilization approaches face problems such as the requirement of tedious multi-step procedures, loss of enzyme activity during immobilization, and poor reusability. In this study, we chose poly-L-lysine (Ki) as a catalyst for silica mineralization and attempted a one-step "leave to stand" synthesis method under mild conditions, so as to simultaneously maintain both high enzymatic activity and reusability. To examine the effect of Kx on the enzymatic reaction of lipase, we performed hydrolysis of 2-octylacetate without adding a silica precursor. Results indicate that Kx hardly exerts adverse influence on the enzymatic activity of lipase. The lipase encapsulated in the silica gel prepared by leave to stand (Gelstand) retained 70% of the activity compared to the free solution, which is two times higher than that obtained by mixing (Gelmix). However, the Km value was found to be similar to that of free enzymes. These results suggest that the leave to stand is a suitable procedure for immobilization, without any decrease in the mass transfer of substrate. The Gel-stand sample retained 100% activity even after the 5th cycle, and retained above 95% of its activity after 4 h of heat treatment at 65 ℃. Using phenyltri-ethoxysilane as a silica precursor, tertiary structural stability of enzyme was obtained, and its Kcat value was improved when compared to a free solution.