title: The sodium cycle in methanogenesis. CO2 reduction to the formaldehyde level in methanogenic bacteria is driven by a primary electrochemical potential of Na+ generated by formaldehyde reduction to CH4.
abstract: CH4 formation from CO2 and H2 rather than from formaldehyde and H2 in methanogenic bacteria is inhibited by uncouplers, indicating that CO2 reduction to the formaldehyde level is energy-driven. We report here that in Methanosarcina barkeri the driving force is a primary electrochemical sodium potential (delta mu Na+) generated by formaldehyde reduction to CH4. This is concluded from the following findings. 1. CO2 reduction to CH4 was insensitive towards protonophores, when the Na+/H+ antiporter was inhibited; under these conditions delta mu Na+ was 120 mV (inside negative), whereas both delta mu H+ and the cellular ATP content were low. 2. CO2 reduction to CH4, rather than formaldehyde reduction, was sensitive towards Na+ ionophores, which dissipated delta mu Na+. 3. CO2 reduction to CH4, in the presence of protonophores and Na+/H+ antiport inhibitors, was coupled with the extrusion of 1-2 mol Na+/mol CH4, and formaldehyde reduction to CH4 was coupled with the extrusion of 3-4 mol Na+/mol CH4. Thus during CO2 reduction to the formaldehyde level 2-3 mol Na+ were consumed.
authors.affiliation: Fachbereich Biologie-Mikrobiologie, Philipps-Universität Marburg, FRG.
authors.forename: B
authors.initials: B
authors.lastname: Kaesler
authors.forename: P
authors.initials: P
authors.lastname: Schönheit
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D019605:Euryarchaeota / Q000378:metabolism; D005557:Formaldehyde / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D008697:Methane / Q000378:metabolism*; D010084:Oxidation-Reduction; D012458:Salicylanilides / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D012458:Salicylanilides; D015222:Sodium Channels; D017923:Sodium-Hydrogen Exchangers; D002245:Carbon Dioxide; D005557:Formaldehyde; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; C003390:3,3',4',5-tetrachlorosalicylanilide; D008697:Methane; C039614:ethylisopropylamiloride