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