Metal-Organic Framework Hybrid Materials of ZIF-8/RGO for Immobilization of D–amino Acid Dehydrogenase

Immobilization of D-amino acid dehydrogenase (DAADH) by the assembly of peptide linker was studied for biosynthesis of D-phenylalanine which is an unnatural amino acid. Hybrid material of ZIF-8 and reduced graphene oxide (RGO) were applied for the immobilization of DAADH from Ureibacillus thermosphaericus. Activity of DAADH/ZIF-8/RGO was enhanced by 1.65 folds than free enzyme. DAADH/ZIF-8/RGO remained 53.4% of its initial activity at 50 °C for 10 h. At the same time the free enzyme was inactivated. The result indicated that the immobilization greatly improved the thermostability of DAADH and the stability in hyperalkaline solution. Kinetic parameters indicated that DAADH/ZIF-8/RGO had greater affinity of phenylpyruvate as Vm /Km of DAADH/ZIF-8/RGO was 1.27-fold than free enzyme. After seven recycles, the activity of DAADH/ZIF-8/RGO remained 64.3%. Furthermore, one step separation and immobilization by ZIF-8/RGO/Ni-DAADH had 1.5-fold activity enhancement. Combination of peptide linker and MOF immobilization, thermostability of the dehydrogenase was significantly improved.