Benzo(a)pyrene (BaP) is one of the polycyclic aromatic hydrocarbons that are found in crude oil, coal tar and creosote. At 47% of waste sites containing these materials, BaP has been detected as a soil contaminant at concentrations up to 1300 ppb (Aspelin, A. L. & Grube, A. H., 2000, in Report 733-R-99 C001, U.S. Environmental Protection Agency, Office of Pesticide Programs, Washington, DC.). There is evidence for BaP carcinogenicity from animal tests, and it is classified as a compound that is probably carcinogenic to humans (Georgian et al., 1983).
BaP degradation pathways have been studied in the Gram-positive bacteria Mycobacterium sp. RJGII-135M (Schneider et al., 1996), M. vanbaalenii (Moody et al., 2004), and the Gram-negative bacterium Sphingomonas yanoikuyae B8/36 (formerly Beijerinckia sp. strain B8/36) (Gibson, 1999). The pathways are initiated by mono- or di-oxygenation at different positions, followed by dehydration of the resulting dihydrodiols, and then oxidative cleavage, usually at the meta-position. Cleavage products are then decarboxylated to form chrysene derivatives. Sphingomonas sp. CHY-1 can grow on chrysene as its sole carbon and energy source (Willison 2004). M. vanbaalenni, in addition to cleaving the benzo(a)pyrene vic-diols formed by dehydration, can methylate their hydroxyl groups.
The following is a text-format benzo(a)pyrene pathway map. An organism which can initiate the pathway is 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 format.
Graphical Map (22 K) | Graphical Map (20 K) Benzo(a)pyrene Benzo(a)pyrene Benzo(a)pyrene Benzo(a)pyrene Benzo(a)pyrene M. vanbaalenii M. vanbaalenii M. vanbaalenii S. yanoikuyae B8/36 Mycobacterium sp. RJGII-135 PYR-1 PYR-1 PYR-1 | | | | | | benzo(a)pyrene | benzo(a)pyrene | benzo(a)pyrene | naphthalene | benzo(a)pyrene | 11,12-epoxidase | cis-11,12- | cis-4,5- | 1,2-dioxygenase | cis-7,8- | | dioxygenase | dioxygenase | | dioxygenase | | | | | | | | | | | | | | | | | | | | v v v v v [Benzo(a)pyrene-] Benzo(a)pyrene- Benzo(a)pyrene- Benzo(a)pyrene- Benzo(a)pyrene- [11,12-epoxide] cis-11,12- cis-4,5- cis-9,10- cis-7,8- | dihydrodiol dihydrodiol dihydrodiol dihydrodiol | | | | | | | | | | | benzo(a)pyrene- | benzo(a)pyrene- | benzo(a)pyrene- | 1,2-dihydroxy- | 7,8-dihydroxy- | 11,12-epoxide | cis-11,12- | cis-4,5- | 1,2-dihydro- v benzo(a)pyrene | hydrolase | dihydrodiol | dihydrodiol | naphthalene | dioxygenase | | dehydrogenase | dehydrogenase | dehydrogenase | | | | | | | | | | | v | v v v Benzo(a)pyrene- | [4,5-Dihydroxy-] [9,10-Dihydroxy-] cis-4- trans-11,12- | [benzo(a)pyrene] [benzo(a)pyrene] (7-Hydroxypyren-8-yl)- dihydrodiol | /| M. vanbaalenii PYR-1 2-oxobut-3-enoate | | / | | | | benzo(a)pyrene- | / | 4,5-dihydroxy- | 9,10-dihydroxy- | | trans-11,12- | / | benzo(a)pyrene | benzo(a)pyrene | C | dihydrodiol | / | dioxygenase | dioxygenase | | dehydrogenase | / | | | | | / | | | | | / | | | | | / | | | v | / | v v [11,12-Dihydroxy-]<---------+ / | cis-4- 7,8-Dihydro-pyrene-8- [benzo(a)pyrene] / | (8-Hydroxypyren-7-yl)- carboxylate | / | 2-oxobut-3-enoate | / | | \ | 11,12-dihydroxy- / | | cis-4-(8- \ | benzo(a)pyrene / | | hydroxy- \ | methyltransferase / 4,5-dihydroxy- | | pyren-7-yl)- \ B | / benzo(a)pyrene | | 2-oxobut-3- \ | /methyltransferase | | enoate lyase \ | / | | \ v / | v v Hydroxymethoxy- <------/ | 10-Oxabenzo- 7,8-Dihydro-pyrene- benzo(a)pyrene | (def)chrysen-9-one 7-carboxylate | | | | | hydroxymethoxy- | | benzo(a)pyrene | | methyltransferase | | | | | | | v v Dimethoxy- 4,5-Chrysene- benzo(a)pyrene dicarboxylate / \ / \ 4,5-chrysene- / \ 4,5-chrysene- dicarboxylate / \ dicarboxylate decarboxylase / \ decarboxylase / \ / \ / \ v v Chrysene-4- Chrysene-5- carboxylate carboxylate | | | | v D v E | | | | v v CO2 CO2
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