Photogeneration of NADPH by oligothiophenes coupled with ferredoxin- NADP reductase

The photogeneration of nicotinamide adenine dinucleotide hydrophosphate (NADPH) and its associated reaction were studied in a novel photo-energy conversion system. The system was composed of the oligothiophene, dimethyl- 4,4'-bipyridinium (MV²⁺), EDTA, and combined with ferredoxin-NADP reductase (FDR, E.C.1.18.1.2). The NADPH was generated by the FDR catalysis via the reduction of MV²⁺ by the photocatalysis of oligothiophene and EDTA as the sacrificial electron donor. As a result, the rate of the NADPH generation depended on the concentrations of nicotinamide adenine dinucleotide phosphate (NADP⁺) and MV²⁺. The effect of the intension of applied light showed the same tendency. Rate values of photoreduction of MV²⁺ and photogeneration of NADPH systems were investigated as a function of the concentration of MV²⁺. The production rates of methyl viologen radical cation (MV⁺) were a 1000- fold more than the NADPH production rates in the oligothiophenes. These results suggest that the electron transfer between FDR and its substrates is the rate-determining step.