Mimic of the Cellular Antioxidant Defense System for a Sustainable Regeneration of Nicotinamide Adenine Dinucleotide (NAD).

The prolonged use of enzymes under oxidative stress is a major challenge in enabling effective enzymatic reaction pathways. Herein, we report a biomimetic antioxidant defensive strategy capable of providing adequate protection of enzymes against superoxide-mediated oxidation. Superoxide dismutase (SOD) and catalase (CAT) were chosen as scavengers and covalently encapsulated into silica nanoreactors, together with glucose dehydrogenase (GDH), which simultaneously should produce the coenzyme nicotinamide adenine dinucleotide (NADH, reduced form). By the enzymatic reactions of SOD and CAT, the interior of silica nanoreactors becomes a "ROS safe zone" to protect the glucose-dependent NADH production of coencapsulated GDH. We further combined this protected NADH-producing module with photocatalytic nanoparticles that enable the light-triggered oxidation of NADH back to NAD (oxidized form). In combination, these two modules allow interconversion between NAD and NADH by the addition of glucose or by light irradiation (LED lamp or sunlight). This protection and regeneration strategy is a versatile tool for enzyme applications for biological reactors, catalysis, or prototypes of artificial organelles or building blocks that contains fragile biomolecules and rely on the coenzyme NAD/NADH.