Co-Authors:
Klughammer, C., Julius-von-Sachs-Institut für Biowissenschaften mit Botanischem Garten, Universität Würzbur Germany, Regensburg, 93053, Germany
Hager, C., Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Fakultät Biologie und Vorklinische Medizin, Universität Regensburg, Regensburg, 93053, Germany
Padan, E., Division of Microbial and Molecular Ecology, Institute of Life Sciences, The Hebrew University of Jerusalem, Israel
Schütz, M., Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Fakultät Biologie und Vorklinische Medizin, Universität Regensburg, Regensburg, 93053, Germany
Schreiber, U., Julius-von-Sachs-Institut für Biowissenschaften mit Botanischem Garten, Universität Würzbur Germany, Regensburg, 93053, Germany
Shahak, Y., Institute of Horticulture, The Volcani Center, ARO, Bet-Dagan, Israel
Hauska, G., Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Fakultät Biologie und Vorklinische Medizin, Universität Regensburg, Regensburg, 93053, Germany
Abstract:
Reduction of cytochromes in chlorosome-free membranes of Chlorobia was studied anaerobically, with an LED array spectrophotometer. For Chlorobium tepidum these membranes contained 0.2 moles cytochrome per mole of bacteriochlorophyll a. The observed change upon complete reduction of oxidized membranes with dithionite could be satisfactorily fitted with three cytochrome components having absorption peaks at 553 (cyt c), 558 and 563 nm (cyt b), in relative amounts of 5:1:2. About 20% of total cytochrome 553 were reducible by ascorbate. Menaquinol reduced all of the 553-component, and this reduction was sensitive to stigmatellin, NQNO and antimycin A. The reduction was insensitive to KCN. However, it was transient at low concentrations of menaquinol in the absence of KCN, but permanent in its presence, demonstrating that electron transport into an oxidation pool was blocked. The 563-component was only slightly reduced by menaquinol unless NQNO or antimycin were present. The stimulation of cytochrome 563-reduction by these inhibitors was more pronounced in the presence of ferricyanide. This phenomenon reflects 'oxidant-induced reduction' of cytochrome b and demonstrates that a Q-cycle is operative in Chlorobia. Also, sulfide fully reduced cytochrome 553, but more slowly than menaquinol. KCN inhibited in this case, as did stigmatellin, NQNO and antimycin A. NQNO was a better inhibitor than antimycin A. Cytochrome 563 again was hardly reduced unless antimycin A was added. The effect was more difficult to observe with NQNO. This supports the conclusion that sulfide oxidation proceeds via the quinone pool and the cytochrome bc-complex in green sulfur bacteria. © 1995 Kluwer Academic Publishers.
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