Light-dependent activity of bacterial chromatophore coupled nitrogenase

Abstract

Previously we have shown that the chromatophore preparation of Rs.rubrum is able to reduce NAD$^+$ photochemically through the direct electron transfer to the ferredoxin coupled NAD$^+$ -oxidoreductase system. On the while, it has also been reported that there exists a nitrogenase system in the crude cell extract of the same bacteria Rs. rubrum, but its reductive activity for nitrogen fixation is found to be light-independent rather it requires other electron donors as in the case of the known nitrogenase system. In this paper, we wish to report our new finding that by mixing the bacterial chromatophore preparation with the crude extract of nitrogenase, the light induced reductive activity of nitrogenase could be demonstrated in the presence of exogenous electron donors such as succinate or DCPIP. This light dependent generation of reductant could be occurred by noncyclic electron transfer, and was electron donor dependent. We also observed that pyruvate served as electron donor for nitrogenase in the dark. From a series of kinetic experiments it was suggested that the bacterial chromatophore was able to couple with a high potential reductive enzyme system so that it performs photochemical reductive processes like a hydrogenation reaction.