Fig.5
3.5 Optimal pH
The optimal pH value of DAADH in pH range of 8.5-12 was investigated. As
shown in Fig.6, optimal pH for free enzyme was 10.0, while the activity
was only 56.3% under pH 11. For immobilized enzyme, the optimal pH was
11.0, which indicated that the immobilized enzymes are robust in the
alkaline solution. Moreover, DAADH/ZIF-8/RGO can maintain a relative
activity of 70.5% with pH 12. The results indicated that the
immobilized carrier (ZIF-8/RGO) can protect the structure of the enzyme
under high alkaline conditions.
Many reported MOFs-enzyme composites exhibit unprecedented catalytic
performances than those of free enzymes, including improved enzyme
stability and recyclability, due to the protection of enzymes by highly
ordered frameworks [9].