Enzyme‐Loaded Nanoreactors Enable the Continuous Regeneration of Nicotinamide Adenine Dinucleotide in Artificial Metabolisms

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme for numerous biocatalytic pathways. While in nature, NAD(+) is continuously regenerated from NADH by enzymes, all synthetic NAD(+) regeneration strategies require a continuous supply of expensive reagents and generate byproducts, making these strategies unattractive. In contrast, we present an artificial enzyme combination that produces NAD(+) from oxygen and water continuously; no additional organic substrates are required once a minimal amount pyruvate is supplied. Three enzymes, i.e., LDH, LOX, and CAT, are covalently encapsulated into a substrate‐permeable silica nanoreactor by a mild fluoride‐catalyzed sol–gel process. The enzymes retain their activity inside of the nanoreactors and are protected against proteolysis and heat. We successfully used NAD(+) from the nanoreactors for the continuous production of NAD(+) i) to sense glucose in artificial glucose metabolism, and ii) to reduce the non‐oxygen binding methemoglobin to oxygen‐binding hemoglobin. This latter conversion might be used for the treatment of Methemoglobinemia. We believe that this versatile tool will allow the design of artificial NAD(+)‐dependent metabolisms or NAD(+)‐mediated redox‐reactions.