Fig.7

3.7 Thermostability study

The thermostability of free enzyme and immobilized enzyme at 50 ℃ was investigated (Fig.8). The reductive amination activity of the immobilized enzymes has declined gradually over time. After incubation for 10h, DAADH/ZIF-8/RGO still retained 53.4% relative enzyme activity and had good thermostability stability. The residual enzyme activity of DAADH/ZIF-8 system was 37.8% while the free enzyme was almost inactivated. The results showed that immobilization improve thermostability stability of DAADH.
The enhancement of thermostability probably due to interaction between peptide and MOF which may restrict the conformational change of DAADH. The dissociation of subunit was prevented by cage effect of MOF immobilization. With large specific surface area, functional diversity and precise control of the particle size, MOFs are ideal carrier with biocompatible microenvironments for enzyme immobilization [26, 27].