Immobilization of d-allulose 3-epimerase into magnetic metal–organic framework nanoparticles for efficient biocatalysis.

d-allulose is a rare low-calorie sugar that has many fundamental biological functions. d-allulose 3-epimerase from Agrobacterium tumefaciens (AT-DAEase) catalyzes the conversion of d-fructose to d-allulose. The enzyme has attracted considerable attention because of its mild catalytic properties. However, the bioconversion efficiency and reusability of AT-DAEase limit its industrial application. Magnetic metal–organic frameworks (MOFs) have uniform pore sizes and large surface areas and can facilitate mass transport and enhance the capacity for enzyme immobilization. Here, we successfully encapsulated cobalt-type AT-DAEase into the cobalt-based magnetic MOF ZIF-67@Fe3O4 using a self-assembly strategy. We confirmed the immobilization of enzyme AT-DAEase and characterized the enzymatic properties of the MOF-immobilized AT-DAEase@ZIF-67@Fe3O4. The AT-DAEase@ZIF-67@Fe3O4 nanoparticles had higher catalytic activity (65.1 U mg−1) and bioconversion ratio (38.1%) than the free AT-DAEase. The optimal conditions for maximum enzyme activity of the AT-DAEase@ZIF-67@Fe3O4 nanoparticles were 55 °C and pH 8.0, which were significantly higher than those of the free AT-DAEase (50 °C and pH 7.5). The AT-DAEase@ZIF-67@Fe3O4 nanoparticles displayed significantly improved thermal stability and excellent recycling performance, with 80% retention of enzyme activity at a temperature range of 45–70 °C and > 45% of its initial activity after eight cycles of enzyme use. The AT-DAEase@ZIF-67@Fe3O4 nanoparticles have great potential for large-scale industrial preparation of d-allulose by immobilizing cobalt-type AT-DAEase into magnetic MOF ZIF-67@Fe3O4. [ABSTRACT FROM AUTHOR]