The three presently known enzymes responsible for arsenic-using bioenergetic processes are arsenite oxidase (Aio), arsenate reductase (Arr) and alternative arsenite oxidase (Arx), all of which are molybdoenzymes from the vast group referred to as the Mo/W-bisPGD enzyme superfamily. Since arsenite is present in substantial amounts in hydrothermal environments, frequently considered as vestiges of primordial biochemistry, arsenite-based bioenergetics has long been predicted to be ancient. Conflicting scenarios, however, have been put forward proposing either Arr/Arx or Aio as operating in the ancestral metabolism. Phylogenetic data argue in favor of Aio whereas biochemical and physiological data led several authors to propose Arx/Arr as the most ancient anaerobic arsenite metabolizing enzymes. Here we combine phylogenetic approaches with physiological and biochemical experiments to demonstrate that the Arx/Arr enzymes could not have been functional in the Archaean geological eon. We propose that Arr reacts with menaquinones to reduce arsenate whereas Arx reacts with ubiquinone to oxidize arsenite, in line with thermodynamic considerations. The distribution of the quinone biosynthesis pathways, however, clearly indicates that the ubiquinone pathway is recent. An updated phylogeny of Arx furthermore reinforces the hypothesis of a recent emergence of this enzyme. We therefore conclude that anaerobic arsenite redox conversion in the Archaean must have been performed in a metabolism involving Aio.

目前引起砷利用生物能过程的三种酶是亚砷酸氧化酶（Aio），砷酸还原酶（Arr）和替代性亚砷酸氧化酶（Arx），所有这些酶都是来自称为Mo / W- bis的庞大群体中的钼酶。PGD​​酶超家族。由于亚砷酸盐大量存在于热液环境中，通常被认为是原始生物化学的痕迹，因此长期以来一直以砷为基础的生物能学被认为是古老的。然而，有人提出了相互矛盾的设想，提出Arr / Arx或Aio在祖先代谢中起作用。系统发育学数据支持Aio，而生化和生理学数据使数位作者提出Arx / Arr是最古老的厌氧亚砷酸盐代谢酶。在这里，我们将系统发育方法与生理和生化实验相结合，以证明Arx / Arr酶在古生地质时代中可能无法发挥作用。我们建议Arr与甲萘醌反应以还原砷，而Arx与泛醌反应以氧化砷，符合热力学考虑。然而，醌生物合成途径的分布清楚地表明泛醌途径是最近的。Arx更新的系统发育进一步强化了这种酶最近出现的假设。因此，我们得出结论，古细菌中的厌氧砷氧化还原转化必须在涉及Aio的新陈代谢中进行。