title: Hydrogen-oxidizing electron transport components in the hyperthermophilic archaebacterium Pyrodictium brockii.
abstract: The hyperthermophilic archaebacterium Pyrodictium brockii grows optimally at 105 degrees C by a form of metabolism known as hydrogen-sulfur autotrophy, which is characterized by the oxidation of H2 by S0 to produce ATP and H2S. UV-irradiated membranes were not able to carry out the hydrogen-dependent reduction of sulfur. However, the activity could be restored by the addition of ubiquinone Q10 or ubiquinone Q6 to the UV-damaged membranes. A quinone with thin-layer chromatography migration properties similar to those of Q6 was purified by thin-layer chromatography from membranes of P. brockii, but nuclear magnetic resonance analysis failed to confirm its identity as a ubiquinone. P. brockii quinone was capable of restoring hydrogen-dependent sulfur reduction to UV-irradiated membranes. Hydrogen-reduced-minus-air-oxidized absorption difference spectra on membranes revealed absorption peaks characteristic of c-type cytochromes. A c-type cytochrome with alpha, beta, and gamma peaks at 553, 522, and 421 nm, respectively, was solubilized from membranes with 0.5% Triton X-100. Pyridine ferrohemochrome spectra confirmed its identity as a c-type cytochrome, and heme staining of membranes loaded on sodium dodecyl sulfate gels revealed a single heme-containing component of 13 to 14 kDa. Studies with the ubiquinone analog 2-n-heptyl-4-hydroxyquinoline-N-oxide demonstrated that the P. brockii quinone is located on the substrate side of the electron transport chain with respect to the c-type cytochrome. These first characterizations of the strictly anaerobic, presumably primitive P. brockii electron transport chain suggest that the hydrogenase operates at a relatively high redox potential and that the H2-oxidizing chain more closely resembles those of aerobic eubacterial H2-oxidizing bacteria than those of the H2-metabolizing systems of anaerobes or the hyperthermophile Pyrococcus furiosus.
authors.affiliation: Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
authors.forename: T D
authors.initials: TD
authors.lastname: Pihl
authors.forename: L K
authors.initials: LK
authors.lastname: Black
authors.forename: B A
authors.initials: BA
authors.lastname: Schulman
authors.forename: R J
authors.initials: RJ
authors.lastname: Maier
mesh_terms: D001105:Archaea / Q000201:enzymology* / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000201:enzymology* / Q000378:metabolism; D003574:Cytochrome c Group / Q000032:analysis; D006358:Hot Temperature; D006859:Hydrogen / Q000378:metabolism*; D006862:Hydrogen Sulfide / Q000378:metabolism; D006864:Hydrogenase / Q000032:analysis; D006912:Hydroxyquinolines / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D008566:Membranes / Q000737:chemistry / Q000201:enzymology; D009532:Nickel / Q000378:metabolism; D011809:Quinones / Q000032:analysis; D013053:Spectrophotometry; D013455:Sulfur / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D003574:Cytochrome c Group; D006912:Hydroxyquinolines; D011809:Quinones; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D013455:Sulfur; D009532:Nickel; D006859:Hydrogen; D007501:Iron; D006864:Hydrogenase; D006862:Hydrogen Sulfide