Resolution of the aerobic respiratory system of the thermoacidophilic archaeon, Sulfolobus sp strain 7 .1. The archaeal, terminal oxidase supercomplex is a functional fusion of respiratory complexes III and IV with no c-type cytochromes

The aerobic respiratory system of the thermoacidophilic archaeon, Sulfolobus sp. strain 7, is unusual in that it consists of only a- and b-type cytochromes but no c-type cytochromes. In previous studies, a novel cytochrome oxidase a(583)-aa(3) subcomplex has been purified, which showed a ferrocytochrome c oxidase but no caldariellaquinol oxidase activity (Wakagi, T., Yamauchi, T., Oshima, T., Muller, M., Azzi, A., and Sone, N. (1989) Biochem. Biophys. Res. Commun, 165, 1110-1114), We show here that the cytochrome subcomplex could be copurified with a non CO-reactive cytochrome b(562) as a novel terminal oxidase ''supercomplex,'' which also contained a Rieske-type FeS cluster at g(y) = 1.89. It contained one copper and all four heme centers detectable in the archaeal membranes by the low temperature spectrophotometry and the potentiometric titration: cytochromes b(562) (+146 mV), a(583) (+270 mV), and aa(3) (+117 and +325 mV). The presence of one copper atom indicates that it contains the conventional heme a(3)-Cu-B binuclear center for reducing molecular oxygen. In conjunction with the presence of a Rieske-type FeS center, inhibitor studies suggest that the terminal oxidase segment of the respiratory chain of Sulfolobus sp, strain 7 is a functional fusion of respiratory complexes III and IV, where cytochrome b(562) and the Rieske-type FeS center probably play a central role in the oxidation of caldariellaquinol. This archaeal terminal oxidase supercomplex reconstitutes the in vitro succinate oxidase respiratory chain for the first time together with caldariellaquinone and the purified cognate succinate:caldariellaquinone oxidoreductase complex. The reconstitution system requires caldariellaquinone for the activity, and is highly sensitive to cyanide and 2-heptyl-4-hydroxy-quinoline-N-oxide, These results are also discussed in terms of the evolutionary considerations.