SULFUR OXIDATION AND REDUCTION IN ARCHAEA - SULFUR OXYGENASE REDUCTASE AND HYDROGENASES FROM THE EXTREMELY THERMOPHILIC AND FACULTATIVELY ANAEROBIC ARCHAEON DESULFUROLOBUS-AMBIVALENS/

The sulfur-dependent, chemolithotrophic, extremely thermophilic, acido philic, and facultatively anaerobic Archaeon Desulfurolobus ambivalens was examined for enzymes involved in energy metabolism. A soluble sul fur oxygenase/-reductase (SOR) was purified and characterized. This en zyme was not detectable in anaerobically grown cells. It produced simu ltaneously sulfite and HIS from sulfur in the presence of oxygen and i s part of the sulfur-oxidizing pathway of the organism. The gene encod ing the single subunit was cloned, sequenced and transcriptionally ana lyzed. Hydrogenase activities were found in cytoplasmic and membrane f ractions of aerobically and of anaerobically grown cells. In non-denat uring gels six different protein bands with hydrogenase activity were detected. The membrane-bound hydrogenase of anaerobically grown cells was investigated in detail, and the presence and distribution of sulfu r reductases, rhodaneses and cytochromes were analyzed. The results of this study are compared to other sulfur-metabolizing enzymes from Arc haea and models of sulfur oxidation and reduction pathways are discuss ed.