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 the biosynthesis of D-phenylalanine. Hybrid material of zeolitic imidazolate framework-8 (ZIF-8) combined with reduced graphene oxide (RGO) was applied for the immobilization of DAADH from Ureibacillus thermosphaericus. The recovery rate of DAADH/ZIF-8/RGO was 165.6%. DAADH/ZIF-8/RGO remained 53.4% of its initial activity at 50 °C for 10 h while the free enzyme was inactivated. DAADH/ZIF-8/RGO maintained 70.5% activity in hyperalkaline solution with pH 12. Kinetic parameters indicated that DAADH/ZIF-8/RGO had greater affinity of phenylpyruvate as V_max/K_m 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 in situ immobilization of DAADH by ZIF-8/RGO/Ni was carried out with 1.5-fold activity enhancement. Combining peptide linker and metal-organic framework (MOF) immobilization, thermostability and activity of the immobilized DAADH were significantly improved.