Abstract
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.
Highlights
A high level of reactive oxygen species (ROS) causes severe damages to live cells due to their high reactivity.[1]
We recently developed photocatalytic nanoparticles based on conjugated microporous polymers (CMPs) that catalyzed the oxidation of NADH to nicotinamide adenine dinucleotide (NAD)+ through a visible-light-triggered production of superoxide.[29]
When NADH was produced by glucose dehydrogenase (GDH), i.e., by simultaneous addition of glucose and irradiation, the oxidation of Amplex red was inhibited as it competed with NADH (Figure 4b)
Summary
A high level of reactive oxygen species (ROS) causes severe damages to live cells due to their high reactivity.[1]. As the silica matrix is an additional barrier for diffusion, we believe any singlet oxygen that could be produced during the light-irradiation would not reach the enzymes inside the nanoreactors because of its extremely short lifetime in water (τ = 3.1−4.5 μs).[31] As a result, the interior of the nanoreactors could be regarded as a “ROS safe zone” by the reactions of nanoconfined SOD/CAT and the silica barrier, enabling effective protection of GDH from ROS-mediated damages and NADH production. When MDA-MB-231 as a model cell line was treated with GSC@nanoreactors and CMP-NPs and irradiated with visible light (460 nm), the cells were successfully protected from the CMP-mediated oxidation because of the scavenging effect of NADH (Figure 4d). The combination of the GSC@nanoreactors together with photocatalytic systems was able to protect living cells and might be expanded to other biological systems, e.g., artificial cellular organelles
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