The missing enzymatic link in syntrophic methane formation from fatty acids.

The microbial production of methane from organic matter is an essential process in the global carbon cycle and an important source of renewable energy. It involves the syntrophic interaction between methanogenic archaea and bacteria that convert primary fermentation products such as fatty acids to the methanogenic substrates acetate, H, CO, or formate. While the concept of syntrophic methane formation was developed half a century ago, the highly endergonic reduction of CO to methane by electrons derived from β-oxidation of saturated fatty acids has remained hypothetical.

Enantioselective Enzymatic Naphthoyl Ring Reduction.

Birch reductions of aromatic hydrocarbons by means of single-electron-transfer steps depend on alkali metals, ammonia, and cryogenic reaction conditions. In contrast, 2-naphthoyl-coenzyme A (2-NCoA) and 5,6-dihydro-2-NCoA (5,6-DHNCoA) reductases catalyze two two-electron reductions of the naphthoyl-ring system to tetrahydronaphthoyl-CoA at ambient temperature. Using a number of substrate analogues, we provide evidence for a Meisenheimer complex-analogous intermediate during 2-NCoA reduction, whereas the subsequent reduction of 5,6-dihydro-2-NCoA is suggested to proceed via an unprecedented cationic transition state.

Two distinct old yellow enzymes are involved in naphthyl ring reduction during anaerobic naphthalene degradation.

The 2-naphthoyl-coenzyme A (NCoA) reductase (NCR) is so far the only characterized enzyme involved in the anaerobic degradation of the environmentally relevant polycyclic aromatic hydrocarbons. The old yellow enzyme (OYE) family member apparently reduced the nonactivated naphthyl ring to 5,6,7,8-tetrahydro-2-napthoyl-CoA (THNCoA). In this work, the candidate genes of three NCRs from the sulphate-reducing, naphthalene-degrading N47 and NaphS2 cultures were expressed in Escherichia coli.

Glutaryl-coenzyme A dehydrogenase from Geobacter metallireducens - interaction with electron transferring flavoprotein and kinetic basis of unidirectional catalysis.

Glutaryl-CoA dehydrogenases (GDHs) are FAD containing acyl-CoA dehydrogenases that usually catalyze the dehydrogenation and decarboxylation of glutaryl-CoA to crotonyl-CoA with an electron transferring flavoprotein (ETF) acting as natural electron acceptor. In anaerobic bacteria, GDHs play an important role in the benzoyl-CoA degradation pathway of monocyclic aromatic compounds. In the present study, we identified, purified and characterized the benzoate-induced BamOP as the electron accepting ETF of GDH (BamM) from the Fe(III)-respiring Geobacter metallireducens.

Identification and characterization of 2-naphthoyl-coenzyme A reductase, the prototype of a novel class of dearomatizing reductases.

The enzymatic dearomatization of aromatic ring systems by reduction represents a highly challenging redox reaction in biology and plays a key role in the degradation of aromatic compounds under anoxic conditions. In anaerobic bacteria, most monocyclic aromatic growth substrates are converted to benzoyl-coenzyme A (CoA), which is then dearomatized to a conjugated dienoyl-CoA by ATP-dependent or -independent benzoyl-CoA reductases. It was unresolved whether or not related enzymes are involved in the anaerobic degradation of environmentally relevant polycyclic aromatic hydrocarbons (PAHs).

Carbon dioxide fixation in 'Archaeoglobus lithotrophicus': are there multiple autotrophic pathways?

Several representatives of the euryarchaeal class Archaeoglobi are able to grow facultative autotrophically using the reductive acetyl-CoA pathway, with 'Archaeoglobus lithotrophicus' being an obligate autotroph. However, genome sequencing revealed that some species harbor genes for key enzymes of other autotrophic pathways, i.e.

Labeling and enzyme studies of the central carbon metabolism in Metallosphaera sedula.

Metallosphaera sedula (Sulfolobales, Crenarchaeota) uses the 3-hydroxypropionate/4-hydroxybutyrate cycle for autotrophic carbon fixation. In this pathway, acetyl-coenzyme A (CoA) and succinyl-CoA are the only intermediates that can be considered common to the central carbon metabolism. We addressed the question of which intermediate of the cycle most biosynthetic routes branch off.