Hydrogen oxidation by membranes from autotrophically grown Alcaligenes eutrophus H16: role of the cyanide-resistant path
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© Springer-Verlag 1996
S H O RT C O M M U N I C AT I O N
Ralph Komen · Karin Schmidt · Davide Zannoni
Hydrogen oxidation by membranes from autotrophically grown Alcaligenes eutrophus H16: role of the cyanide-resistant pathway in energy transduction
Received: 30 October 1995 / Accepted: 17 January 1996
Abstract Eighty percent of the ATP and proton electrochemical gradient (-Z∆pH) formed during H2 oxidation in membranes from autotrophically grown exponentialphase cells of Alcaligenes eutrophus H16 was derived from a redox pathway that includes the membrane-bound hydrogenase complex and the cyanide-resistant (bo-type) oxidase. The H2/ubiquinone-1 oxidoreductase activity was coupled to energy transduction and was fully inhibited by the quinone along 2-n-hepthyl-4-hydroxyquinoline-Noxide. We conclude that the cytochrome-c-containing pathway in exponential-phase A. eutrophus H16 cells plays a minor role in energy conservation. Key words Energy transduction · Hydrogen respiration · Cyanide-resistant oxidase · Membrane-bound hydrogenase · Alcaligenes eutrophus H16 Abbreviation HQNO 2-n-Hepthyl-4-hydroxyquinolineN-oxide
Introduction The hydrogen-oxidizing bacterium Alcaligenes eutrophus is a unique chemolithoautotroph in that it contains two [NiFe] hydrogenases: a membrane-bound enzyme that is connected to the respiratory chain, and a soluble enzyme that reduces NAD+ (H2/NAD+ oxido-reductase; Bowien and Schlegel 1981; Friedrich and Schwartz 1993). Unlike
the case of other chemolithotrophs, e.g., Paracoccus denitrificans, in which electron transport and energy tranduction have been analyzed in detail (Porte and Vignais 1980; Trumpower 1990), limited information is available on the efficiency of energy transduction associated with H2 consumption by autotrophically grown A. eutrophus (Bowien and Schlegel 1981). Early results have suggested the presence of three coupling sites, with no clue to the role of the canide-insensitive pathway (Bongers 1970; Drozd 1977). In recent years, however, various experimental approaches have demonstrated that exponential-phase cells are endowed with three membrane-bound oxidases: two cytochrome c oxidases containing hemes of cb- and atype, which are fully inhibited by 10–4 M KCN, and a third oxidase of the bo-type that is blocked by 5 mM KCN (Komen et al. 1991a, b). This latter oxidase is operationally defined as “KCN-resistant oxidase,” although a fourth d-type oxidase (inhibited by 20 mM KCN) is found in the late-stationary growth phase (Komen et al. 1991a, b). These new acquisitions on the composition and phenotypic expression of the redox branches contributing to the overall respiration of A. eutrophus H16 prompted us to reexamine the bioenergetics of H2 respiration. Here we show that H2 oxidation by membranes from autotrophically grown exponential-phase cells of A. eutrophus H16 is linked to several energy transducing sites. Notably, most of the ∆µH+ is generated by a redox pathway that includes the membrane-bound hydrogenase complex and the bo-type oxidase.
Materials and methods Kom
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