The chemolithoautotrophic archaeon Pyrodictium abyssi isolate TAG 11 lives close to 100°C and gains energy by sulfur respiration, with hydrogen as electron donor. From the membranes of this hyperthermophile, an ATPase complex was isolated. The purified enzyme consists of six major polypeptides, the 67, 51, 41, 26 and 22 kDa subunits composing the AF1 headpiece, and the 7 kDa proteolipid of the AF0 component. The headpiece of the enzyme restored the formation of ATP during sulfur respiration in membrane vesicles from which it had been removed by low salt treatment. Characteristics of the reconstituted activity suggest that the same enzyme is responsible for ATP formation in untreated membranes. ATP formation was neither sensitive to ionophores and uncouplers, nor to dicyclohexyl carbodiimide, but depended on closed vesicles. Both ATPase activity (up to 2 μmol per min and mg protein) as well as ATP formation (up to 0.4 μmol per min and mg membrane protein) were highest at 100°C. A P/e2 ratio of close to one can be estimated for sulfur respiration with hydrogen. In addition to ATP, autoradiographic detection revealed the formation of high quantities of 33Pi-labeled ADP and of another compound not identified so far.
