title: Hydrogen formation from glycolate driven by reversed electron transport in membrane vesicles of a syntrophic glycolate-oxidizing bacterium.
abstract: Oxidation of glycolate to 2 CO2 and 3 H2 (delta G degrees' = +36 kJ/mol glycolate) by the proton-reducing, glycolate-fermenting partner bacterium of a syntrophic coculture (strain FlGlyM) depends on a low hydrogen partial pressure (pH2). The first reaction, glycolate oxidation to glyoxylate (E zero' = -92 mV) with protons as electron acceptors (E zero' = -414 mV), is in equilibrium only at a pH2 of 1 microPa which cannot be maintained by the syntrophic partner bacterium Methanospirillum hungatei; energy therefore needs to be spent to drive this reaction. Glycolate dehydrogenase activity (0.3-0.96 U.mg protein-1) was detected which reduced various artificial electron acceptors such as benzyl viologen, methylene blue, dichloroindophenol, K3[Fe(CN)6], and water-soluble quinones. Fractionation of crude cell extract of the glycolate-fermenting bacterium revealed that glycolate dehydrogenase, hydrogenase, and proton-translocating ATPase were membrane-bound. Menaquinones were found as potential electron carriers. Everted membrane vesicles of the glycolate-fermenting bacterium catalyzed ATP-dependent H2 formation from glycolate (30-307 nmol H2.min-1 x mg protein-1). Protonophores, inhibitors of proton-translocating ATPase, and the quinone analog antimycin A inhibited H2 formation from glycolate, indicating the involvement of proton-motive force to drive the endergonic oxidation of glycolate to glyoxylate with concomitant H2 release. This is the first demonstration of a reversed electron transport in syntrophic interspecies hydrogen transfer.
authors.affiliation: Fakultät für Biologie, Universität Konstanz, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Friedrich
authors.forename: B
authors.initials: B
authors.lastname: Schink
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000255:Adenosine Triphosphate / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004579:Electron Transport; D005285:Fermentation; D006016:Glycolates / Q000378:metabolism*; D006094:Gram-Positive Bacteria / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D017013:Methanobacteriaceae / Q000378:metabolism; D010084:Oxidation-Reduction; D011809:Quinones / Q000378:metabolism / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology; D014812:Vitamin K / Q000378:metabolism
chemical_list: D006016:Glycolates; D011809:Quinones; D014475:Uncoupling Agents; C031149:glycolic acid; D014812:Vitamin K; D006859:Hydrogen; D000255:Adenosine Triphosphate; D000429:Alcohol Oxidoreductases; C020819:glycolic acid dehydrogenase; D000251:Adenosine Triphosphatases