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MICB 301: Final Wikipedia Article Submission (Assignment #5)
Submitted on Nov. 19, 2017

Methane Production
Methanogens are known to produce methane from substrates such as H2/CO2, acetate, formate, methanol and methylamines in a process called methanogenesis. 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.

H2/CO2 Methanogenesis
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. These organism are typically found in anaerobic environments.

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.

(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.

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. 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.

(Formation of methane)

(Regeneration of coenzyme M)

Fermentative metabolism
The understanding of methanogen metabolism has progressed steadily since the 1930s.

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

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


 * CH3COO− + H+ &rarr; CH4 + CO2      &Delta;G° = -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
Methanogens are known to produce methane from substrates such as H2/CO2, acetate, formate, methanol and methylamines in a process called methanogenesis. 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.

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.

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

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