Characterization of denitrifying enzymes in photosynthetic bacterium

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Rhodobacter sphaeroides f. sp. denitrificans IL 106 is the first isolated strain as a photosynthetic denitrifying bacteria, which can grow depending on a variety of energy-generating systems, i.e., not only denitrification, but also O_2 respirarion, dimethyl sulfoxide respiration and photosynthesis.Denitrifying enzymes in this photosynthetic bacterium,were studied. Nitrous oxide reductase (N_2OR), nitrite reductase (NIR) and nitric oxide reductase (NOR) were examined. Especially, N_2OR was intensively studied and characterized.The N_2OR from this strain was purified by ammonium sulfate fractionation, gel filtration chromatography and anion exchange chromatography. This purified enzyme is composed of two identical subunits and contains four copper atoms per subunit. The subunit molecular mass was 66 kDa determined by MALDI-TOF-MS. By means of ESR measurement, this enzyme contains at least three types of copper centers, namely, CU_A, Cuz_1 and Cuz_3. The CU_A center, which is different from Cu(type 1) or Cu(type 2) and found only in N_2OR and cytochrome oxidase, was found in this enzyme and supposed to play a role in electron transfer.