Superoxide is a reactive oxygen species produced during aerobic metabolism in mitochondria and prokaryotes. It causes damage to lipids, proteins and DNA and is implicated in cancer, cardiovascular disease, neurodegenerative disorders and aging. As protection, cells express soluble superoxide dismutases, disproportionating superoxide to oxygen and hydrogen peroxide. Here, we describe a membrane-bound enzyme that directly oxidizes superoxide and funnels the sequestered electrons to ubiquinone in a diffusion-limited reaction. Experiments in proteoliposomes and inverted membranes show that the protein is capable of efficiently quenching superoxide generated at the membrane in vitro. The 2.0 Å crystal structure shows an integral membrane di-heme cytochrome b poised for electron transfer from the P-side and proton uptake from the N-side. This suggests that the reaction is electrogenic and contributes to the membrane potential while also conserving energy by reducing the quinone pool. Based on this enzymatic activity, we propose that the enzyme family be denoted superoxide oxidase (SOO).

超氧化物是线粒体和原核生物有氧代谢过程中产生的一种活性氧。它会对脂质、蛋白质和 DNA 造成损害，并与癌症、心血管疾病、神经退行性疾病和衰老有关。作为保护，细胞表达可溶性超氧化物歧化酶，将超氧化物歧化为氧气和过氧化氢。在这里，我们描述了一种膜结合酶，它直接氧化超氧化物并在扩散限制反应中将隔离的电子漏斗到泛醌。蛋白脂质体和倒置膜的实验表明，该蛋白质能够有效地淬灭体外膜上产生的超氧化物。2.0 Å 晶体结构显示了一个完整的膜二血红素细胞色素b准备从P侧和从N侧吸收质子。这表明该反应是生电的并且有助于膜电位，同时还通过减少醌池来保存能量。基于这种酶活性，我们建议将该酶家族称为超氧化物氧化酶 (SOO)。