Ubiquinone Oxidoreductase (1.3V)

Regeneration of enzymatic cofactors is the most significant technical hurdle preventing the widespread employment of biochemical synthetic reactions as a production process for fine chemical manufacturing. The high cost of the continual replacement of enzymatic cofactors limits the economic viability of this production methodology despite potentially significant improvements in product quality and an associated reduction in environmental impact. Presented is an engineered biotic/abiotic organelle system that works to address this limitation. This system reduces nicotinamide coenzymes using light for energy. It sources the required electrons from water and generates oxygen as the sole by-product. This is accomplished by coupling two complex …show more content…
Attempts of constructing a photobioreactor through the pairing biocatalysis cycle with photocatalysis, despite their progression over recent years still pale in efficiency to nature(6). Many of these technologies fail to provide the oxidation power necessary to oxidize water (1.3V). Presented here is a novel, biologically engineered construct that circumvents many of the pitfalls associated with enzymatic regeneration of NADH. The vectoral integration of Photosystem II (PSII) and Respiratory Complex I (CMI) (NADH:Ubiquinone oxidoreductase) into liposomes results in an artificial organelle capable of NAD+ photoreduction (Fig. 1). Photons harvested by PSII result in water oxidation generating oxygen and protons as part of the process. The electrons from water are transferred to ubiquinone (Q) producing ubiquinol (QH2) (7, 8). The accumulation of protons generates a proton motive force (PMF); essential to diminish the thermodynamic gap of the standard redox potentials between NADH/NAD+ and QH2/Q to permit reverse electron transfer (RET) from QH2 to NAD+ by CMI(9) . By coupling the associated metabolisms of these two enzymes NADH is produced using light and water as substrates with oxygen as the only …show more content…
The preparations yielded consistent results, with an average maximum NAD+ photoreduction rate of 354.85 38.71 (mean S.E.) nmol min-1 mg CMI-1(Fig. 3,A). Comparing the production rates of H+ to NADH, it is possible to calculate the coupling efficiency of the two enzymes using the reaction stoichiometry of 5H+ to produce a one NADH molecule. During the reaction PSII produces H+ at 4.36 0.79 nmol min-1 (16), whereas CMI is responsible for their consumption at -1.77 0.19 nmol min-1 yielding a coupling efficiency of 38.32% 10.80%. We postulate the remainder of unused H+ could be accounted for by the protons required to generate the PMF together with protons produced by PSII molecules reconstituted in the incorrect orientation and proton leakage across the vesicle