Sodium ion-dependent hydrogen production in Acidaminococcus fermentans |
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Authors: | Ulrich Härtel W Buckel |
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Institution: | Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universit?t, D-35032 Marburg, Germany Tel. +49–6421–281527; Fax +49-6421-288979 e-mail: buckel@mailer.uni-marburg.de, DE
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Abstract: | Acidaminococcus fermentans is able to ferment glutamate to ammonia, CO2, acetate, butyrate, and H2. The molecular hydrogen (approximately 10 kPa; E′ = –385 mV) stems from NADH generated in the 3-hydroxybutyryl-CoA dehydrogenase reaction (E°′ = –240 mV) of the hydroxyglutarate pathway. In contrast to growing cells, which require at least 5 mM Na+, a Na+-dependence of the H2-formation was observed with washed cells. Whereas the optimal glutamate fermentation rate was achieved already at 1 mM Na+, H2 formation commenced only at > 10 mM Na+ and reached maximum rates at 100 mM Na+. The acetate/butyrate ratio thereby increased from 2.0 at 1 mM Na+ to 3.0 at 100 mM Na+. A hydrogenase and an NADH dehydrogenase, both of which were detected in membrane fractions, are components of a model in
which electrons, generated by NADH oxidation inside of the cytoplasmic membrane, reduce protons outside of the cytoplasmic
membrane. The entire process can be driven by decarboxylation of glutaconyl-CoA, which consumes the protons released by NADH
oxidation inside the cell. Hydrogen production commences exactly at those Na+ concentrations at which the electrogenic H+/Na+-antiporter glutaconyl-CoA decarboxylase is converted into a Na+/Na+ exchanger.
Received: 3 May 1996 / Accepted: 12 August 1996 |
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Keywords: | Acidaminococcus fermentans Glutamate fermentation Glutaconate production Hydrogenase Reversed electron transport NADH dehydrogenase Na+ bioenergetics Glutaconyl-CoA decarboxylase |
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