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Benzoate (or benzoyl-CoA) is the most common intermediate in anaerobic metabolism of aromatic compounds. In the absence of molecular oxygen, the aromatic ring is first reduced prior to ring cleavage. Benzoate is activated to benzoyl-CoA. Dearomatization of the benzene ring is occurs upon a 2 electron reduction of benzoyl-CoA to cyclohex-diene-1-carboxyl-CoA. For subsequent oxidation of cyclohex-diene-1-carboxyl-CoA to 3-hydroxypimelyl-CoA, two metabolic routes are currently discussed, one which involves cyclohex-1-ene-1-carboxyl-CoA as intermediate and another which involves 6-hydroxy-cyclohex-1-ene-1-carboxyl-CoA. For more specific information, see Harwood and Gibson (1998) and Koch et al (1993). Most studies of anaerobic benzoate degradation have been carried out with the phototrophic bacterium Rhodopseudomonas palustris and with two denitrifying species, Thauera aromatica K172 and Azoarcus evansii (formerly Pseudomonas sp. strain K 172 and KB 740, respectively).
Activities of cyclohex-1-ene-1-carboxyl-CoA hydratase, 2-hydroxycyclohexane-1-carboxyl-CoA dehydrogenase and 2-ketocyclohexane-1-carboxyl-CoA hydrolase were not demonstrated directly. The left side of the reactions from 6-Hydroxycyclohex-1-ene-1-carboxyl-CoA to 3-Hydroxypimelyl-CoA is proposed and has not been identified experimentally. The Pimelyl-CoA degradation from Pimelyl-CoA to Acetyl-CoA is also proposed and most of the enzymes of this sequence do not appear to have been directly assayed.
This page shows only anaerobic pathway of benzoate degradation. Its aerobic degradation is documented elsewhere in the EAWAG-BBD.
The following is a text-format benzoate degradation (anaerobic) pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic form: right branch (13K), left branch (11K), and from 3-Hydroxypimelyl-CoA (10K).
terephthalate decarboxylase Benzoate <--------------- Terephthalate <----+ Thauera aromatica K172 | Rhodopseudomonas palustris | from the Azoarcus evansii from the Anaerobic Phenol | Phthalate Family Pathway \ | Pathway \ | \ | benzoate-CoA \ | ligase from the v v from the Anaerobic Toluene -----> Benzoyl-CoA <----- Anaerobic Ethylbenzene Pathway | and 2-Aminobenzoic acid | benzoyl-CoA Pathways | reductase v Cyclohex-2,5-diene- Cyclohex-1,5-diene- Cyclohex-1,4-diene- 1-carboxyl-CoA <--> 1-carboxyl-CoA <--> 1-carboxyl-CoA / \ cyclohex-1,5-diene- / \ 1-carboxyl-CoA / \ hydratase / \ v v 6-Hydroxycyclohex-1-ene- Cyclohex-1-ene- 1-carboxyl-CoA 1-carboxyl-CoA | | 6-hydroxycyclohex- | | cyclohex-1-ene- 1-ene-1-carboxyl-CoA | | 1-carboxyl-CoA hydratase | | hydratase v v 2,6-Dihydroxycyclohexane- 2-Hydroxycyclohexane- 1-carboxyl-CoA 1-carboxyl-CoA | | 2,6-dihydroxycyclo- | | 2-hydroxycyclohexane- hexane-1-carboxyl-CoA | | 1-carboxyl-CoA dehydrogenase | | dehydrogenase v v 6-Oxo-2-hydroxycyclohexane- 2-Ketocyclohexane- 1-carboxyl-CoA 1-carboxyl-CoA | | 6-oxo-2-hydroxycyclo- | | 2-ketocyclohexane- hexane-1-carboxyl-CoA | | 1-carboxyl-CoA hydrolase | | hydrolase | v | Pimelyl-CoA \ / \ / pimelyl-CoA \ / dehydrogenase \ v \ 2,3-Didehydro-pimeloyl-CoA \ / \ / enoyl-CoA \ / hydratase v v 3-Hydroxypimelyl-CoA | | 3-hydroxypimelyl-CoA | dehydrogenase v 3-Ketopimelyl-CoA | | 3-ketopimelyl-CoA | thiolase v Glutaryl-CoA | | glutaryl-CoA | dehydrogenase v Glutaconyl-CoA | | glutaconyl-CoA | decarboxylase v Crotonoyl-CoA | | enoyl-CoA | hydratase v from the 3-Hydroxyacyl-CoA <------------ Cyclopropanecarboxylate | pathway | acetoacetyl-CoA | reductase v Acetoacetyl-CoA | | acetoacetyl-CoA | thiolase v Acetyl-CoA | | | v Intermediary Metabolism (KEGG)
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