Cofactor NAD(P)H Regeneration: How Selective Are the Reactions?

Precision Engineering of the Co-immobilization of Enzymes for Cascade Biocatalysis

The design and orderly layered co-immobilization of multiple enzymes on resin particles remain challenging. In this study, the SpyTag/SpyCatcher binding pair was fused to the N-terminus of an alcohol dehydrogenase (ADH) and an aldo-keto reductase (AKR), respectively. A non-canonical amino acid (ncAA), p-azido-L-phenylalanine (p-AzF), as the anchor for covalent bonding enzymes, was genetically inserted into preselected sites in the AKR and ADH. Employing the two bioorthogonal counterparts of SpyTag/SpyCatcher and azide-alkyne cycloaddition for the immobilization of AKR and ADH enabled sequential dual-enzyme coating on porous microspheres. The ordered dual-enzyme reactor was subsequently used to synthesize (S)-1-(2-chlorophenyl)ethanol asymmetrically from the corresponding prochiral ketone, enabling the in situ regeneration of NADPH. The reactor exhibited a high catalytic conversion of 74 % and good reproducibility, retaining 80 % of its initial activity after six cycles. The product had 99.9 % ee, which that was maintained in each cycle. Additionally, the double-layer immobilization method significantly increased the enzyme loading capacity, which was approximately 1.7 times greater than that of traditional single-layer immobilization. More importantly, it simultaneously enabled both the purification and immobilization of multiple enzymes on carriers, thus providing a convenient approach to facilitate cascade biocatalysis.

Photoredox catalysis may be a general mechanism in photodynamic therapy

Elucidating the underlying photochemical mechanisms of action (MoA) of photodynamic therapy (PDT) may allow its efficacy to be improved and could set the stage for the development of new classes of PDT photosensitizers. Here, we provide evidence that "photoredox catalysis in cells," wherein key electron transport pathways are disrupted, could constitute a general MoA associated with PDT. Taking the cellular electron donor nicotinamide adenine dinucleotide as an example, we have found that well-known photosensitizers, such as Rose Bengal, BODIPY, phenoselenazinium, phthalocyanine, and porphyrin derivatives, are able to catalyze its conversion to NAD+. This MoA stands in contrast to conventional type I and type II photoactivation mechanisms involving electron and energy transfer, respectively. A newly designed molecular targeting photocatalyst (termed CatER) was designed to test the utility of this mechanism-based approach to photosensitizer development. Photoexcitation of CatER induces cell pyroptosis via the caspase 3/GSDME pathway. Specific epidermal growth factor receptor positive cancer cell recognition, high signal-to-background ratio tumor imaging (SBRTI = 12.2), and good tumor growth inhibition (TGI = 77.1%) are all hallmarks of CatER. CatER thus constitutes an effective near-infrared pyroptotic cell death photo-inducer. We believe the present results will provide the foundation for the synthesis of yet-improved phototherapeutic agents that incorporate photocatalytic chemistry into their molecular design.

Highly Efficient S-g-CN/Mo-368 Catalyst for Synergistically NADH Regeneration Under Solar Light

Sulfur-doped graphitic carbon nitride (S-g-CN) has gained significant attention in recent years. Sulfur-doped graphitic carbon nitride (S-g-CN) is a promising metal-free photocatalyst because of its band orientation, natural abundance and groundwork. Improved photocatalytic activity of S-g-CN material for solar chemical production persists a hot yet challenging problem. Herein, we provide an adaptable method for the synthesis of S-g-CN nanocomposite decorated with the moiety of giant polyoxometalate (S-g-CN/Mo-368) that subsequently showed highly efficient photocatalytic activity. The as-synthesized S-g-CN/Mo-368 as a recyclable artificial photocatalyst revealed excellent activity for solar chemical production, that is nicotinamide adenine dinucleotide (NADH) regeneration under visible light. The immobilized Mo-368 on the S-g-CN surface increased the visible light adsorption capacity of the S-g-CN/Mo-368 photocatalyst. The visible light absorption activity, morphology, element compositions, particle size and zeta potential of S-g-CN powder and S-g-CN/Mo-368 were thoroughly investigated. From the application point of view, S-g-CN/Mo-368 was applied to determine the solar chemical production (i.e. NADH regeneration) under visible light with a higher yield% of about ~ 94.85%.

Copper oxide-based cathode for direct NADPH regeneration

Nearly a fourth of all enzymatic activities is attributable to oxidoreductases, and the redox reactions supported by this vast catalytic repertoire sustain cellular metabolism. In many biological processes, reduction depends on hydride transfer from either reduced nicotinamide adenine dinucleotide (NADH) or its phosphorylated derivative (NADPH). Despite longstanding efforts to regenerate NADPH by various methods and harness it to support chemoenzymatic synthesis strategies, the lack of product purity has been a major deterrent. Here, we demonstrate that a nanostructured heterolayer Ni-Cu₂O-Cu cathode formed by a photoelectrochemical process has unexpected efficiency in direct electrochemical regeneration of NADPH from NADP⁺. Remarkably, two-thirds of NADP⁺ was converted to NADPH with no measurable production of the inactive (NADP)₂ dimer and at the lowest reported overpotential [- 0.75 V versus Ag/AgCl (3 M NaCl) reference]. Sputtering of nickel on the copper-oxide electrode nucleated an unexpected surface morphology that was critical for high product selectivity. Our results should motivate design of integrated electrolyzer platforms that deploy this heterogeneous catalyst for direct electrochemical regeneration of NADH/NADPH, which is central to design of next-generation biofuel fermentation strategies, biological solar converters, energy-storage devices, and artificial photosynthesis.