Friedrich M, Schink B. Hydrogen formation from glycolate driven by reversed electron transport in membrane vesicles of a syntrophic glycolate-oxidizing bacterium.
EUROPEAN JOURNAL OF BIOCHEMISTRY 1993;
217:233-40. [PMID:
8223560 DOI:
10.1111/j.1432-1033.1993.tb18238.x]
[Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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.
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