Characterization of denitrifying enzymes in photosynthetic bacterium

类球红杆菌f. sp. acetificans IL 106是作为光合细菌的第一个分离的菌株，其可以依赖于各种能量产生系统生长，即，对该光合细菌的反硝化酶、O_2呼吸、二甲基亚砜呼吸和光合作用进行了研究。测定了一氧化氮还原酶（NOR）、亚硝酸盐还原酶（NIR）和一氧化氮还原酶（N_2OR）。对N_2OR进行了深入的研究和表征，并通过硫酸铵分级沉淀、凝胶过滤层析和阴离子交换层析对该菌株的N_2OR进行了纯化。这种纯化的酶由两个相同的亚基组成，每个亚基含有四个铜原子。MALDI-TOF-MS测定亚基分子量为66 kDa。ESR测定表明，该酶至少含有3种铜中心，即CU_A、Cuz_1和Cuz_3。在该酶中发现了与Cu（1型）或Cu（2型）不同的、仅存在于N_2OR和细胞色素氧化酶中的CU_A中心，推测它可能在电子传递中起作用。

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.