title: Novel insights into the bioenergetics of mixed-acid fermentation: can hydrogen and proton cycles combine to help maintain a proton motive force?
abstract: Escherichia coli possesses four [NiFe]-hydrogenases that catalyze the reversible redox reaction of 2H(+) + 2e(-) ↔ H2. These enzymes together have the potential to form a hydrogen cycle across the membrane. Their activity, operational direction, and interaction with each other depend on the fermentation substrate and particularly pH. The enzymes producing H2 are likely able to translocate protons through the membrane. Moreover, the activity of some of these enzymes is dependent on the F0 F1 -ATPase, thus linking a proton cycle with the cycling of hydrogen. These two cycles are suggested to have a primary basic role in modulating the cell's energetics during mixed-acid fermentation, particularly in response to pH. Nevertheless, the mechanisms underlying the physical interactions between these enzyme complexes, as well as how this is controlled, are still not clearly understood. Here, we present a synopsis of the potential impact of proton-hydrogen cycling in fermentative bioenergetics.
authors: Department of Microbiology, Plants and Microbes Biotechnology, Faculty of Biology, Yerevan State University, Yerevan, Armenia.
authors: Armen
authors: A
authors: Trchounian
authors: R
authors: R
authors: Gary Sawers
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D004734:Energy Metabolism; D005285:Fermentation / Q000502:physiology*; D006859:Hydrogen; D018892:Proton-Motive Force; D011522:Protons
chemical_list: D011522:Protons; D006859:Hydrogen
keywords: Escherichia coli; F0F1-ATPase; bioenergetics; fermentation; hydrogen cycle; hydrogenases; proton cycle