Several aspects of the proposal, which aims to expand open access, require serious discussion and, in some cases, a rethink.
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Edited by Douglas C. Rees, California Institute of Technology, Pasadena, CA, and approved April 29, 2003 (received for review March 12, 2003)
Article Figures & SI
Figures
- Fig. 1.
Model of chemiosmotic coupling between the MBH and the ATP synthase in intact cells of P. furiosus. Fdred and Fdox represent the reduced (by oxidative metabolism) and oxidized forms of the redox protein Fd, respectively. Fdred is reoxidized by the MBH, which reduces H+ to produce H2. As the primary proton-translocating complex, MBH also pumps H+ across the membranes, resulting in a transmembrane proton gradient. This gradient can then be used by the secondary proton translocating complex, ATPase, to produce ATP. See text for details, and note that experiments were conducted with inverted vesicles.
- Fig. 2.
ATPase and hydrogen evolution activities of washed membrane vesicles of P. furiosus. Enzyme activities were measured as described in Materials and Methods. Fd was used as the electron carrier for H2 production. ATPase activity is specifically inhibited by DCCD and nitrate but not by azide. The membrane-bound hydrogenase activity is specifically inhibited by copper ions (CuCl2).
- Fig. 3.
Hydrogen production and ATP synthesis catalyzed simultaneously by membrane vesicles. Enzyme activities were measured as described in Materials and Methods. Fd or MV was used as the electron carrier for H2 production. Membrane vesicles synthesize ATP and produce H2 in the presence of either Fd or MV as electron carriers (complete). MBH-coupled ATP synthesis is not observed either in the absence of the electron donor (–DT) for H2 production or if the MBH is inhibited (+CuCl2). ATP is not produced in the presence of ATP-synthase inhibitors (+DCCD, +nitrate) or in the absence of the pmf (+CCCP).
- Fig. 4.
Direct measurements of ΔpH and Δψ during hydrogen production. The change in pH (a and b) was measured by using acridine orange, and the change in electrochemical potential (c and d) was measured by using oxonol VI as described in Materials and Methods. ΔpH (a) and Δψ (c) are formed when the electron donor Fd is added to the vesicles. Δψ and ΔpH are collapsed by the addition of CCCP (a and c) and when the MBH is inhibited by copper ions (CuCl2, d), and these also prevent formation of ΔpH.
- Fig. 5.
Hydrogen oxidation driven by reverse proton pumping. H2 uptake activity was measured by using benzyl viologen (BV) or MV as the electron acceptor as described in Materials and Methods. The activity is stimulated by the presence of ATP (+ATP) but is unaffected by ADP and Pi [+(ADP + Pi)] or when the ATPase is inhibited by nitrate (+nitrate).
- Fig. 6.
Pathways of electron flow and energy conservation during sugar catabolism by P. furiosus. G-6-P, glucose 6-phosphate; F-6-P, fructose 6-phosphate; F-1,6-bP, fructose 1,6-bisphosphate; GAPOR, GAP:Fd oxidoreductase; 3-PG, 3-phosphoglycerate; 2-PG, 2-phosphoglycerate; PEP, phosphoenolpyruvate; POR, pyruvate:Fd oxidoreductase; ACS, acetyl-CoA synthase. See text for details.
A simple energy-conserving system: Proton reduction coupled to proton translocation
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