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MICB 301: Final Wikipedia Article Submission (Assignment #5)[edit]

Submitted on Nov. 19, 2017

Methane Production[edit]

Methanogens are known to produce methane from substrates such as H2/CO2, acetate, formate, methanol and methylamines in a process called methanogenesis. [1] Different methanogenic reactions are catalyzed by unique sets of enzymes and coenzymes. While reaction mechanism and energetics vary between one reaction and another, all of these reactions contribute to net positive energy production by creating ion concentration gradients that are used to drive ATP synthesis.[2]

H2/CO2 Methanogenesis[edit]

The overall reaction for H2/CO2 methanogenesis is:


(∆G˚’ = -134 kJ/mol CH4)


Well-studied organisms that produce methane via H2/CO2 methanogenesis include Methanosarcina barkeri, Methanobacterium thermoautotrophicum, and Methanobacterium wolfei.[3][4][5]These organism are typically found in anaerobic environments.[1]


In the earliest stage of H2/CO2 methanogenesis, CO2 binds to methylfuran (MF) and is reduced to formyl-MF. This endergonic reductive process (∆G˚’= +16 kJ/mol) is dependent on the availability of H2 and is catalyzed by the enzyme formyl-MF dehydrogenase.[1]


The formyl constituent of formyl-HF is then transferred to the coenzyme tetrahydromethanopterin (H4MPT) and is catalyzed by a soluble enzyme known as formyl transferase. This results in the formation of formyl-H4MPT.[1]


Formyl-H4MPT is subsequently reduced to methenyl-H4MPT. Methenyl-H4MPT then undergoes a one-step hydrolysis followed by a two-step reduction to methyl-H4MPT. The two-step reversible reduction is assisted by coenzyme F420 whose hydride acceptor spontaneously oxidizes.[1] Once oxidized, F420’s electron supply is replenished by accepting electrons from H2. This step is catalyzed by methylene H4MPT dehydrogenase.[6]


(Formyl-H4MPT reduction)

(Methenyl-H4MPT hydrolysis)

(H4MPT reduction)


Next, the methyl group of methyl-M4MPT is transferred to coenzyme M via a methyltransferase-catalyzed reaction.[7][8]


The final step of H2/CO2 methanogenic involves methyl-coenzyme M reductase and two coenzymes: N-7 mercaptoheptanoylthreonine phosphate (HS-HTP) and coenzyme F430. HS-HTP donates electrons to methyl-coenzyme M allowing the formation of methane and mixed disulfide of HS-CoM.[9] F430, on the other hand, serves as a prosthetic group to the reductase. H2 donates electrons to the mixed disulfide of HS-CoM and regenerates coenzyme M.[10]


(Formation of methane)

(Regeneration of coenzyme M)


References[edit]

  1. ^ a b c d e Blaut, M. (1994). "Metabolism of methanogens". Antonie Van Leeuwenhoek. 66 (1–3): 187–208. ISSN 0003-6072. PMID 7747931.
  2. ^ Dybas, M; Konisky, J (1992). "Energy transduction in the methanogen Methanococcus voltae is based on a sodium current". J Bacteriol. 174(17): 5575–5583.
  3. ^ Karrasch, M.; Börner, G.; Enssle, M.; Thauer, R. K. (1990-12-12). "The molybdoenzyme formylmethanofuran dehydrogenase from Methanosarcina barkeri contains a pterin cofactor". European Journal of Biochemistry. 194 (2): 367–372. ISSN 0014-2956. PMID 2125267.
  4. ^ Börner, G.; Karrasch, M.; Thauer, R. K. (1991-09-23). "Molybdopterin adenine dinucleotide and molybdopterin hypoxanthine dinucleotide in formylmethanofuran dehydrogenase from Methanobacterium thermoautotrophicum (Marburg)". FEBS letters. 290 (1–2): 31–34. ISSN 0014-5793. PMID 1915887.
  5. ^ Schmitz, Ruth A.; Albracht, Simon P. J.; Thauer, Rudolf K. (1992-11-01). "A molybdenum and a tungsten isoenzyme of formylmethanofuran dehydrogenase in the thermophilic archaeon Methanobacterium wolfei". European Journal of Biochemistry. 209 (3): 1013–1018. doi:10.1111/j.1432-1033.1992.tb17376.x. ISSN 1432-1033.
  6. ^ Zirngibl, C (February 1990). "N5,N10-Methylenetetrahydromethanopterin dehydrogenase from Methanobacterium thermoautotrophicum has hydrogenase activity". Laboratorium fir Mikrobiologie. 261(1): 112–116.
  7. ^ te Brömmelstroet, B. W.; Geerts, W. J.; Keltjens, J. T.; van der Drift, C.; Vogels, G. D. (1991-09-20). "Purification and properties of 5,10-methylenetetrahydromethanopterin dehydrogenase and 5,10-methylenetetrahydromethanopterin reductase, two coenzyme F420-dependent enzymes, from Methanosarcina barkeri". Biochimica Et Biophysica Acta. 1079 (3): 293–302. ISSN 0006-3002. PMID 1911853.
  8. ^ Kengen, Servé W. M.; Mosterd, Judith J.; Nelissen, Rob L. H.; Keltjens, Jan T.; Drift, Chris van der; Vogels, Godfried D. (1988-08-01). "Reductive activation of the methyl-tetrahydromethanopterin: coenzyme M methyltransferase from Methanobacterium thermoautotrophicum strain ΔH". Archives of Microbiology. 150 (4): 405–412. doi:10.1007/BF00408315. ISSN 0302-8933.
  9. ^ Bobik, T. A.; Olson, K. D.; Noll, K. M.; Wolfe, R. S. (1987-12-16). "Evidence that the heterodisulfide of coenzyme M and 7-mercaptoheptanoylthreonine phosphate is a product of the methylreductase reaction in Methanobacterium". Biochemical and Biophysical Research Communications. 149 (2): 455–460. ISSN 0006-291X. PMID 3122735.
  10. ^ Ellermann, J.; Hedderich, R.; Böcher, R.; Thauer, R. K. (1988-03-15). "The final step in methane formation. Investigations with highly purified methyl-CoM reductase (component C) from Methanobacterium thermoautotrophicum (strain Marburg)". European Journal of Biochemistry. 172 (3): 669–677. ISSN 0014-2956. PMID 3350018.


MICB 301: Wikipedia Assignment #3 (Draft of Wikipedia Article) Oct. 8, 2017

Original- "Methanogens"

Fermentative metabolism[edit]

The understanding of methanogen metabolism has progressed steadily since the 1930s.[1]

Although most marine biogenic methane is the result of carbon dioxide (CO2) reduction, a small amount is derived from acetate (CH3COO−) fermentation.[2]

In the fermentation pathway, acetic acid undergoes a dismutation reaction to produce methane and carbon dioxide:[3][4]

CH3COO− + H+ → CH4 + CO2       ΔG° = -36 kJ/reaction

This disproportionation reaction is enzymatically catalysed. One electron is transferred from the carbonyl function (e− donor) of the carboxylic group to the methyl group (e− acceptor) of acetic acid to respectively produce CO2 and methane gas.

Archaea that catabolize acetate for energy are referred to as acetotrophic or aceticlastic. Methylotrophic archaea utilize methylated compounds such as methylamines, methanol, and methanethiol as well.



Edit- "Methanogens"

Methane Production[edit]

Methanogens are known to produce methane from substrates such as H2/CO2, acetate, formate, methanol and methylamines in a process called methanogenesis.[5] Different methanogenic reactions are catalyzed by unique sets of enzymes and coenzymes. While reaction mechanism and energetics vary between one reaction and another, all of these reactions contribute to net positive energy production by creating ion concentration gradients that are used to drive ATP synthesis.[6]


H2/CO2 Methanogenesis

The overall reaction for H2/CO2 methanogenesis is:


CO2 + 4H2 → CH4 + 2H2O (∆G˚’ = -134 kJ/mol CH4)


In the earliest stage of H2/CO2 methanogenesis, CO2 binds to methylfuran (MF) and is reduced to formyl-MF. This endergonic reductive process (∆G˚’= +16 kJ/mol) is dependent on the availability of H2 and is catalyzed by the enzyme formyl-MF dehydrogenase.


The formyl constituent of formyl-HF is then transferred to the coenzyme tetrahydromethanopterin (H4MPT) and is catalyzed by a soluble enzyme known as formyl transferase. This results in the formation of formyl-H4MPT.


Formyl-H4MPT is subsequently reduced to methenyl-H4MPT. Methenyl-H4MPT then undergoes a one-step hydrolysis followed by a two-step reduction to methyl-H4MPT. The two-step reversible reduction is assisted by coenzyme F420 whose hydride acceptor spontaneously oxidizes. Once oxidized, F420’s electron supply is replenished by accepting electrons from H2. This step is catalyzed by methylene H4MPT dehydrogenase.[7]


Next, the methyl group of methyl-M4MPT is transferred to coenzyme M via a methyltransferase-catalyzed reaction.[8][9] The final step of H2/CO2 methanogenic involves methyl-coenzyme M reductase and two coenzymes: N-7 mercaptoheptanoylthreonine phosphate (HS-HTP) and coenzyme F430. HS-HTP donates electrons to methyl-coenzyme M allowing the formation of methane and mixed disulfide of HS-CoM.[10] F430, on the other hand, serves as a prosthetic group to the reductase. H2 donates electrons to the mixed disulfide of HS-CoM and regenerates coenzyme M.[11]


Dbb5012 (talk) 23:02, 8 October 2017 (UTC)

  1. ^ Thauer, R. K. (1998). "Biochemistry of methanogenesis: a tribute to Marjory Stephenson. 1998 Marjory Stephenson Prize Lecture" (Free). Microbiology. 144 (9): 2377–2406. doi:10.1099/00221287-144-9-2377. PMID 9782487.
  2. ^ M.J. Whiticar; et al. (1986). "Biogenic methane formation in marine and freshwater environments: CO2 reduction vs. acetate fermentation — isotope evidence". Geochim. Cosmochim. Acta. 50 (5): 393–709. Bibcode:1986GeCoA..50..693W. doi:10.1016/0016-7037(86)90346-7.
  3. ^ Ferry, J.G. (1992). "Methane from acetate". Journal of Bacteriology. 174 (17): 5489–5495. PMC 206491. PMID 1512186. Retrieved 2011-11-05.
  4. ^ Vogels, G.D.; Keltjens J.T.; Van Der Drift C. (1988). "Biochemistry of methane production". In Zehnder A.J.B. (ed.). Biology of anaerobic microorganisms. New York: Wiley. pp. 707–770.
  5. ^ Blaut, Michael (1994). "Metabolism of Methanogens". Antonie van Leeuwenhoek. 66 (1–3): 187–208.
  6. ^ Dybas, M; Konisky, J (1992). "Energy transduction in the methanogen Methanococcus voltae is based on a sodium current". Journal of Bacteriology. 174 (17).
  7. ^ Blaut, Michael (1994). "Metabolism of Methanogens". Antonie van Leeuwenhoek. 66 (1–3): 187–208.
  8. ^ van der Meijden, P; te Brömmelstroet, BW; Poirot, CM; van der Drift, C; Vogels, GD (1984). "Purification and properties of methanol:5-hydroxybenzimidazolylcobamide methyltransferase from Methanosarcina barkeri". J Bacteriol. 160 (2): 629–635.
  9. ^ Kengen, Servé; Judith, Mosterd; Rob, Nelissen; Jan, Keltjens; Chris, van der Drift; Godfried, Vogels (1988). "Reductive activation of the methyl-tetrahydromethanopterin: coenzyme M methyltransferase from Methanobacterium thermoautotrophicum strain ΔH". Archives of Microbiology. 150 (4): 405–412.
  10. ^ Thomas, Bobik; Karl, Olson; Kenneth, Noll; Ralph, Wolfe (1987). "Evidence that the heterodisulfide of coenzyme M and 7-mercaptoheptanoylthreonine phosphate is a product of the methylreductase reaction in Methanobacterium". Biochemical and Biophysical Research Communications. 140 (2): 455–460.
  11. ^ Ellermann, J; Hedderich, R; Böcher, R; Thauer, RK (1988). "The final step in methane formation. Investigations with highly purified methyl-CoM reductase (component C) from Methanobacterium thermoautotrophicum (strain Marburg)". The FEBS Journal. 172 (3): 669–677.
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