Abstract
The first enzyme of the denitrification in Rhodobacter sphaeroides f. sp. denitrificans is located in the periplasm. The nitrate reductase genes consist of napKEFDABC. NapC containing tetra heme c is thought to be an electron carrir between quinol and the nitrate reductase. An activating signal regulating expression of the nap operon is not clear at all.
By assaying β-galactosidade activity from napKEFD-lacZ fusions, relationships between growth conditions and the signal generation in the wild type strain and nap mutants were studied. Under anaerobic-dark conditions with nitrate, the LacZ activity was the highest, and rather lowered by light. However, even under aerobic conditions without nitrate, the activity was high. In the napA and napB mutant strains, little LacZ activity was observed, showing that nitrate was not the signal. In the napC mutant, both high LacZ and nitrate reductase activities were observed.
