Sodium ion pumps and hydrogen production in glutamate fermenting anaerobic bacteria.
Anaerobic bacteria ferment glutamate via two different pathways to ammonia, carbon dioxide, acetate, butyrate and molecular hydrogen. The coenzyme B12-dependent pathway in Clostridium tetanomorphum via 3-methylaspartate involves pyruvate:ferredoxin oxidoreductase and a novel enzyme, a membrane-bound NADH:ferredoxin oxidoreductase. The flavin- and iron-sulfur-containing enzyme probably uses the energy difference between reduced ferredoxin and NADH to generate an electrochemical Na+ gradient, which drives transport processes. The other pathway via 2-hydroxyglutarate in Acidaminococcus fermentans and Fusobacterium nucleatum involves glutaconyl-CoA decarboxylase, which uses the free energy of decarboxylation to generate also an electrochemical Na+ gradient. In the latter two organisms, similar membrane-bound NADH:ferredoxin oxidoreductases have been characterized. We propose that in the hydroxyglutarate pathway these oxidoreductases work in the reverse direction, whereby the reduction of ferredoxin by NADH is driven by the Na+ gradient. The reduced ferredoxin is required for hydrogen production and the activation of radical enzymes. Further examples show that reduced ferredoxin is an agent, whose reducing energy is about 1 ATP 'richer' than that of NADH.
Boiangiu
Clara D
CD
Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Marburg, Germany.
Jayamani
Elamparithi
E
Brügel
Daniela
D
Herrmann
Gloria
G
Kim
Jihoe
J
Forzi
Lucia
L
Hedderich
Reiner
R
Vgenopoulou
Irini
I
Pierik
Antonio J
AJ
Steuber
Julia
J
Buckel
Wolfgang
W
D000595:Amino Acid Sequence; D001421:Bacteria, Anaerobic / Q000201:enzymology*; D001693:Biological Transport, Active; D005971:Glutamates / Q000378:metabolism*; D005977:Glutarates / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D016623:Ion Pumps / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism
D005971:Glutamates; D005977:Glutarates; D016623:Ion Pumps; C019417:alpha-hydroxyglutarate; D006859:Hydrogen; D012964:Sodium