Fig. 4: The thermodynamic and spatial ranges of nicotinamide cofactor recycling.
From: Interactive biocatalysis achieved by driving enzyme cascades inside a porous conducting material
a A free energy profile for electron/hydride transfer from an electrode to a reactant undergoing catalytic reduction at dehydrogenase E2. Transfers indicated in green are favourable, and those in red are unfavourable. b The >100-fold nanoconfinement advantage, showing the current measured at increasing concentrations of NADP(H) in solution. The black curve shows results with FNR (E1) and isocitrate dehydrogenase (E2) loaded but without isocitrate in the solution. The current depends on the FNR-catalysed oxidation of NADPH entering the ITO layer from the solution. The red trace shows results with the two-enzyme cascade reaction activated by adding isocitrate (10 mM): the current now depends on the rate of localised NADP(H) recycling. A rotating disc electrode, held at +0.2 V vs SHE, was used in each case. The data focus on conditions where NADPH < 10 mM to emphasise the regime that shows the largest enhancement. c Localised recycling between crowded enzymes: FNR, IDH1, and NADP(H) drawn to-scale with an FNR-IDH1 mean centre-to-centre distance of 9.4 Å, equivalent to a combined concentration of 2 mM (see text). Panel b was adapted with permission41.
