Free methanogenic

The third type of hydrogenases from some methanogenic archea, also referred to as iron-sulfur-cluster-free hydrogenase, oxHmd, has attracted interest in bioinorganic... 

Methanogens, may be the Earth s oldest organisms, produce methane from carbon dioxide and hydrogen. They can survive only in an anaerobic (i.e., oxygen-free) environment and have been found in ocean trenches, in mud, in sewage, and in cow s stomachs. 

Proposed mechanism for the reversible reaction of N, N -methenyltetrahydromethanopterin (methenyl-H4MPT ) with H2 to N, N -methylenetetrahydromethanopterin (methylene-H4MPT) and a proton catalysed by the metal-free hydrogenase from methanogenic archaea... 

The metal-free hydrogenase from methanogenic archaea... 

Berkessel, A. and Thauer, R. K. (1995) On the mechanism of catalysis by a metal-free hydro-genase from methanogenic archaea Enzymic transformation of H2 without a metal and its analogy to the chemistry of alkanes in superacidic solution. Angew. Cbem., Int. Ed. Engl., 34, 2247-50. 

Buurman, G., Shima, S., Thauei R. K. (2000) The metal-free hydrogenase from methanogenic archaea evidence for a bound cofactor. FEBS Lett. 485, 200M... 

Geierstanger, B. H., Prasch, T., Griesinger, C., Hartmann, G. C., Buurman, G. and Thauer, R. K. (1998) Catalytic mechanism of the metal-free hydrogenase from Methanogenic Archaea Reversed stereospecificity of the catalytic and non-catalytic reaction. Angew. Chem. Int., 37, 3300-3. 

In flooded soil or sediment, bubbles form through heterogeneous nucleation at the surface of sohd particles, rather than by homogeneous nucleation in free solution. Because of this, bubbles form easily and the sum of the partial pressures of volatile solutes tends to be maintained at or near the hydrostatic pressure. Therefore, for a methanogenic sediment. 

To ensure no oxygen was present, the methanogenic enrichment culture was flushed with oxygen-free gas for 20 min before incubating in the dark at 35 °C. After a 13-d acclimation period, the amount of methane and carbon dioxide produced in 14 d was 63% of theoretical. 

Methanogenic bacteria cannot tolerate oxygen and are restricted to sites that are free of it the rumen of cows provides a good example, as does the mud in rice paddies. 

F430, a yellow, water-soluble compound, was first extracted from boiled cells of methanogenic bacteria, a discovery which Wolfe (19) has credited to J. LeGall. Its isolation was first reported by Gunsalus and Wolfe (83). The cofactor has a Soret band in the visible region at 430 nm. Functionally F430 is a prosthetic group of the methylreductase system (24, 84). It is also found in the free state in cell extracts (85). 

As discussed previously, superelectrophilic activation in biological systems has been found even with a metal-free hydrogenase enzyme found in methanogenic archea, an enzymatic system that converts CO2 to methane.57 It was found that /V5./V10-menthyl tetrahydromethanopterin (42) undergoes an enzyme-catalyzed reaction with H2 by hydride transfer to the pro-R position and release of a proton to form the reduced product (43 eq 36). 

As described in Chapter 2, a unique gitonic superelectrophile is considered to be involved in an enzyme system that converts CO2 to methane. Berkessel and Thauer have studied this metal-free hydrogenase enzyme from methanogenic archaea and a mechanism is proposed involving activation through a vicinal-superelectrophilic system (eq 34).50... 

Glu 6, a major constituent of dissolved free amino acids (DFAA) in marine sediments [71], has been detected in red algae (Rhodophyta) [72] and as a potential osmolyte in several marine bacteria, for example obligatory aerobic heterotrophs [70] and methanogenic archaebacteria [8], N-methyl-/ -glutamate has been reported solely as a natural product from the cyanobacterium Prochloron didemni [96]. 

Lyon EJ, Shima S, Buurman G, Chowdhuri S, Batschauer A, Steinbach K, Thauer RK (2004) UV-A/blue-light inactivation of the metal-free hydrogenase (Hmd) from methanogenic archaea. The enzyme contains functional iron after all. Eur. J. Biochem. 271 195-204... 

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