A new UiO-66-NH₂ MOF-based nano-immobilized DFR enzyme as a biocatalyst for the synthesis of anthocyanidins

Anthocyanidins and anthocyanins are one subclass of flavonoids in plants with diverse biological functions and have health-promoting effects. Dihydroflavonol 4-reductase (DFR) is one of the important enzymes involved in the biosynthesis of anthocyanidins and other flavonoids. Here, a new MOF-based nano-immobilized DFR enzyme acting as a nano-biocatalyst for the production of anthocyanidins in vitro was designed. We prepared UiO-66-NH₂ MOF nano-carrier and recombinant DFR enzyme from genetic engineering. DFR@UiO-66-NH₂ nano-immobilized enzyme was constructed based on covalent bonding under the optimum immobilization conditions of the enzyme/carrier ratio of 250 mg/g, 37 °C, pH 6.5 and fixation time of 10 min. DFR@UiO-66-NH₂ was characterized and its catalytic function for the synthesis of anthocyanidins in vitro was testified using UPLC-QQQ-MS analysis. Compared with free DFR enzyme, the enzymatic reaction catalyzed by DFR@UiO-66-NH₂ was more easily for manipulation in a wide range of reaction temperatures and pH values. DFR@UiO-66-NH₂ had better thermal stability, enhanced adaptability, longer-term storage, outstanding tolerances to the influences of several organic reagents and Zn²⁺, Cu²⁺ and Fe²⁺ ions, and relatively good reusability. This work developed a new MOF-based nano-immobilized biocatalyst that had a good prospect of application in the green synthesis of anthocyanins in the future.