Crystallographic Studies on the Short-lived Respiratory Enzyme-Substrate Complex

一氧化氮合酶(NOR)是一种含铁的酶，催化一氧化氮(NO)还原生成一种主要的温室气体--一氧化二氮(N2O)。在这项研究中，我们报道了铜绿假单胞菌和嗜热脂肪杆菌的cNOR在2.7埃分辨率和2.5埃分辨率下的晶体结构。虽然这些NORs的总体结构与细胞色素氧化酶(COX)密切相关，但没有观察到连接COX活性中心和细胞内空间的D-或K-质子途径。CNOR反应所需的质子可能是从细胞外侧提供的。相反，qNOR具有从细胞质一侧到活性中心的潜在质子通道。

Nitric oxide reductase (NOR) is an iron-containing enzyme that catalyzes the reduction of nitric oxide (NO) to generate a major greenhouse gas, nitrous oxide (N_2O). In this study, we report the crystal structures of cNOR from Pseudomonas aeruginosa at 2.7 angstrom resolution and qNOR from Geobacillus stearothermophilus at 2.5 angstrom resolution. Although the overall structure of these NORs are closely related to cytochrome oxidase (COX), neither the D- nor K-proton pathway, which connect the COX active center to the intracellular space, was observed. Protons required for the cNOR reaction are probably provided from the extracellular side. On the contrary, qNOR has potential proton channel from the cytoplasmic side to the active center.