PURIFICATION AND PROPERTIES OF AN EXTREMELY THERMOSTABLE MEMBRANE-BOUND SULFUR-REDUCING COMPLEX FROM THE HYPERTHERMOPHILIC PYRODICTIUM-ABYSSI

The chemolithoautotrophic archaeon Pyrodictium abyssi isolate TAG 11 g ains energy by reducing sulfur with H-2 to H2S. From this hyperthermop hile, a sulfur-reducing complex catalyzing this reaction was purified 13.5-fold. The native complex exhibited a brownish-yellow colour and s howed an apparent molecular mass of 520 kDa. SDS/PAGE revealed the pre sence of nine different major polypeptides with apparent molecular mas ses of 82, 72, 65, 50, 47, 42, 40, 30 and 24 kDa. The native complex c ontained 50-55 mol acid-labile sulfur, 50-55 mol iron, 1.6 mol nickel. 1.2 mol copper, 2.8 mol cytochrome b and 0.3 mol cytochrome c (all pe r mol native complex). The temperature optimum of the H-2:sulfur oxido reductase complex was 100 degrees C, which is consistent with the phys iological growth optimum of the native organism. The complex is extrem ely heat stable. During 5 h incubation at 100 degrees C, no decrease i n H2S-forming activity could be observed.