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|Title:||Bioenergetics of Methanococcus voltae: Possible role for a primary sodium pump in ATP formation|
|Author(s):||Dybas, Michael James|
|Doctoral Committee Chair(s):||Konisky, Jordan|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The mechanism of ATP formation has been characterized in a few methanogens. Evidence has been obtained in whole cells of Methanosarcina barkeri that ATP is synthesized via a chemiosmotic mechanism. Results obtained with protoplasts from Methanobacterium thermoautotrophicum also agree with a chemiosmotic mechanism of ATP synthesis. Lancaster proposed a mechanism of ATP formation in M. voltae coupled to a novel scheme of substrate level phosphorylation. The mechanisms of ATP formation in M. voltae were examined by biochemical means.
To characterize the terminal step in methane formation and its link to energy conservation in vivo, coenzyme M uptake systems were characterized, and used to deliver CH$\sb3$-S-CoM to cells. When H$\sb2$ is supplied as a reductant, M. voltae is capable of forming methane, a membrane potential, and ATP. By using this CH$\sb3$-S-CoM/H$\sb2$ substrate pair and comparing this to use of H$\sb2$:CO$\sb2$ as substrates for methanogenesis, the terminal reactions of methane formation in vivo, separate from the other reactions of the C$\sb1$ cycle, were characterized.
A primary sodium pump coupled to methane formation in M. voltae, and a Na$\sp+$/H$\sp+$ antiporter activity was characterized. M. voltae was shown to grow utilizing H$\sb2$:CO$\sb2$ as energy substrates in the absence of a proton motive force at alkaline pH. While the sodium pump extrudes sodium ions under slightly alkaline conditions (pH 8.2), neutral conditions and slightly acidic conditions (pH 6.5), ATP synthesis and growth in the absence of a protonmotive force were only found to occur under alkaline conditions, and required a high concentration of sodium ions. ATP formation, methanogenesis, transmembrane pH gradients, protonmotive force, intracellular sodium concentrations, sodium motive force, and phosphorylation potentials were determined in cells grown under extremes of pH and sodium ion concentrations. These observations suggest the possible existence of a sodium based chemiosmotic mechanism of ATP formation in this marine methanogen, which operates at alkaline pH. A P-type ATPase and a V-type ATPase were found in membranes of M. voltae grown under a variety of growth conditions.
These results suggest that energy conservation in vivo occurs linked to the reduction of CH$\sb3$-S-CoM to methane, and occurs via a chemiosmotic mechanism in which the coupling ion at alkaline pH may be sodium.
|Rights Information:||Copyright 1992 Dybas, Michael James|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9215806|