title: ATP-dependent/-independent enzymatic ring reductions involved in the anaerobic catabolism of naphthalene.
abstract: Polycyclic aromatic hydrocarbons are among the most hazardous environmental pollutants. However, in contrast to aerobic degradation, the respective degradation pathways in anaerobes are greatly unknown which has so far prohibited many environmental investigations. In this work, we studied the enzymatic dearomatization reactions involved in the degradation of the PAH model compounds naphthalene and 2-methylnaphthalene in the sulfate-reducing enrichment culture N47. Cell extracts of N47 grown on naphthalene catalysed the sodium dithionite-dependent four-electron reduction of the key intermediate 2-naphthoyl-coenzyme A (NCoA) to 5,6,7,8-tetrahydro-2-naphthoyl-CoA (THNCoA). The NCoA reductase activity was independent of ATP and was, surprisingly, not sensitive to oxygen. In cell extracts in the presence of various electron donors the product THNCoA was further reduced by a two-electron reaction to most likely a conjugated hexahydro-2-naphthoyl-CoA isomer (HHNCoA). The reaction assigned to THNCoA reductase strictly depended on ATP and was oxygen-sensitive with a half-life time between 30 s and 1 min when exposed to air. The rate was highest with NADH as electron donor. The results indicate that two novel and completely different dearomatizing ring reductases are involved in anaerobic naphthalene degradation. While the THNCoA reducing activity shows some properties of ATP-dependent class I benzoyl-CoA reductases, NCoA reduction appears to be catalysed by a previously unknown class of dearomatizing aryl-carboxyl-CoA reductases.
authors: Institute of Biology II, University of Freiburg, Freiburg, Germany.
authors: Christian
authors: C
authors: Eberlein
authors: Jörg
authors: J
authors: Johannes
authors: Housna
authors: H
authors: Mouttaki
authors: Masih
authors: M
authors: Sadeghi
authors: Bernard T
authors: BT
authors: Golding
authors: Matthias
authors: M
authors: Boll
authors: Rainer U
authors: RU
authors: Meckenstock
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000693:Anaerobiosis; D001419:Bacteria / Q000201:enzymology*; D003065:Coenzyme A / Q000378:metabolism; D004785:Environmental Pollutants / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006207:Half-Life; D053858:Metabolic Networks and Pathways; D009281:Naphthalenes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology
chemical_list: D004785:Environmental Pollutants; D009281:Naphthalenes; C031721:naphthalene; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; D010100:Oxygen; C027384:2-methylnaphthalene; D003065:Coenzyme A