Limits...
Rerouting Cellular Electron Flux To Increase the Rate of Biological Methane Production.

Catlett JL, Ortiz AM, Buan NR - Appl. Environ. Microbiol. (2015)

Bottom Line: In Methanosarcina acetivorans, HdrABC expression caused an increased rate of methanogenesis and a decrease in metabolic efficiency on methylotrophic substrates.When acetate was the sole carbon and energy source, neither deletion nor overexpression of HdrABC had an effect on growth or methane production rates.These results suggest that in cells grown on methylated substrates, the cell compensates for energy losses due to expression of HdrABC with an increased rate of substrate turnover and that HdrABC lacks the appropriate electron donor in acetate-grown cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.

No MeSH data available.


Related in: MedlinePlus

Putative models for the role of HdrABC during methylotrophic growth. (A) In an electron confurcation mechanism, HdrABC uses electrons from both FdxH2 and F420H2 in a 1:1 ratio to reduce two molecules of CoM-S-S-CoB and bypasses Rnf, Fpo, and HdrED energy-conserving enzyme complexes. (B) In a direct-reduction mechanism, HdrABC bypasses either Rnf or Fpo ion translocation steps by using FdxH2 or F420H2 as an electron donor. (C) HdrABC uses a bifurcation mechanism to reduce CoM-S-S-CoB while interchanging electrons between FdxH2 and F420H2 electron carriers. The model in panel B most closely matches the experimental data. ka is the rate of HdrABC enzyme activity; kCH4 is the rate of methane production; tg is the generation time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4561719&req=5

Figure 1: Putative models for the role of HdrABC during methylotrophic growth. (A) In an electron confurcation mechanism, HdrABC uses electrons from both FdxH2 and F420H2 in a 1:1 ratio to reduce two molecules of CoM-S-S-CoB and bypasses Rnf, Fpo, and HdrED energy-conserving enzyme complexes. (B) In a direct-reduction mechanism, HdrABC bypasses either Rnf or Fpo ion translocation steps by using FdxH2 or F420H2 as an electron donor. (C) HdrABC uses a bifurcation mechanism to reduce CoM-S-S-CoB while interchanging electrons between FdxH2 and F420H2 electron carriers. The model in panel B most closely matches the experimental data. ka is the rate of HdrABC enzyme activity; kCH4 is the rate of methane production; tg is the generation time.

Mentions: However, because functional hydrogenases are not expressed in M. acetivorans and some other Methanosarcinales species, Vhu or another hydrogenase cannot be the electron donor for HdrABC in these organisms. In light of this fact, it is possible that HdrABC may use one of three general mechanisms for catalysis: an electron confurcation mechanism (defined as when one electron each from two separate donors is transferred to one two-electron acceptor), where electrons from both reduced ferredoxin (FdxH2) and reduced F420 (8-hydroxy-5-deazaflavin [F420H2]) are used to reduce two molecules of CoM-S-S-CoB (Fig. 1A); a direct-reduction mechanism, where either FdxH2 or F420H2 could reduce CoM-S-S-CoB (Fig. 1B); or an electron bifurcation mechanism that couples oxidation of FdxH2 to reduction of both CoM-S-S-CoB and another electron carrier, such as F420 (Fig. 1C). Based on the lack of hydrogenase activity in M. acetivorans and because the reaction would be energetically favorable, HdrABC was thought to use FdxH2 as a substrate to directly reduce CoM-S-S-CoB (Fig. 1B) (8).


Rerouting Cellular Electron Flux To Increase the Rate of Biological Methane Production.

Catlett JL, Ortiz AM, Buan NR - Appl. Environ. Microbiol. (2015)

Putative models for the role of HdrABC during methylotrophic growth. (A) In an electron confurcation mechanism, HdrABC uses electrons from both FdxH2 and F420H2 in a 1:1 ratio to reduce two molecules of CoM-S-S-CoB and bypasses Rnf, Fpo, and HdrED energy-conserving enzyme complexes. (B) In a direct-reduction mechanism, HdrABC bypasses either Rnf or Fpo ion translocation steps by using FdxH2 or F420H2 as an electron donor. (C) HdrABC uses a bifurcation mechanism to reduce CoM-S-S-CoB while interchanging electrons between FdxH2 and F420H2 electron carriers. The model in panel B most closely matches the experimental data. ka is the rate of HdrABC enzyme activity; kCH4 is the rate of methane production; tg is the generation time.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561719&req=5

Figure 1: Putative models for the role of HdrABC during methylotrophic growth. (A) In an electron confurcation mechanism, HdrABC uses electrons from both FdxH2 and F420H2 in a 1:1 ratio to reduce two molecules of CoM-S-S-CoB and bypasses Rnf, Fpo, and HdrED energy-conserving enzyme complexes. (B) In a direct-reduction mechanism, HdrABC bypasses either Rnf or Fpo ion translocation steps by using FdxH2 or F420H2 as an electron donor. (C) HdrABC uses a bifurcation mechanism to reduce CoM-S-S-CoB while interchanging electrons between FdxH2 and F420H2 electron carriers. The model in panel B most closely matches the experimental data. ka is the rate of HdrABC enzyme activity; kCH4 is the rate of methane production; tg is the generation time.
Mentions: However, because functional hydrogenases are not expressed in M. acetivorans and some other Methanosarcinales species, Vhu or another hydrogenase cannot be the electron donor for HdrABC in these organisms. In light of this fact, it is possible that HdrABC may use one of three general mechanisms for catalysis: an electron confurcation mechanism (defined as when one electron each from two separate donors is transferred to one two-electron acceptor), where electrons from both reduced ferredoxin (FdxH2) and reduced F420 (8-hydroxy-5-deazaflavin [F420H2]) are used to reduce two molecules of CoM-S-S-CoB (Fig. 1A); a direct-reduction mechanism, where either FdxH2 or F420H2 could reduce CoM-S-S-CoB (Fig. 1B); or an electron bifurcation mechanism that couples oxidation of FdxH2 to reduction of both CoM-S-S-CoB and another electron carrier, such as F420 (Fig. 1C). Based on the lack of hydrogenase activity in M. acetivorans and because the reaction would be energetically favorable, HdrABC was thought to use FdxH2 as a substrate to directly reduce CoM-S-S-CoB (Fig. 1B) (8).

Bottom Line: In Methanosarcina acetivorans, HdrABC expression caused an increased rate of methanogenesis and a decrease in metabolic efficiency on methylotrophic substrates.When acetate was the sole carbon and energy source, neither deletion nor overexpression of HdrABC had an effect on growth or methane production rates.These results suggest that in cells grown on methylated substrates, the cell compensates for energy losses due to expression of HdrABC with an increased rate of substrate turnover and that HdrABC lacks the appropriate electron donor in acetate-grown cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.

No MeSH data available.


Related in: MedlinePlus