Polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene are commonly found as pollutants in soils, estuarine waters and sediments, and other terrestrial and aquatic sites. Although phenanthrene is not mutagenic or carcinogenic, it has been shown to be toxic to marine diatoms, gastropods, mussels, crustaceans, and fish. Phenanthrene is a tricyclic aromatic hydrocarbon. Since it is the smallest aromatic hydrocarbon to have a "bay-region" and a "K-region", phenanthrene is often used as a model substrate for studies on metabolism of carcinogenic PAHs.
Phenanthrene is degraded by some soil bacteria through one of two different routes. In one route,1-hydroxy-2-naphthoic acid is oxidized to 1,2-dihydroxynaphthalene, which is further degraded via the Naphthalene Pathway to salicylate which can be further metabolized. In the other pathway, the ring of 1-hydroxy-2-naphthoic acid is cleaved and further metabolized via the Phthalate Pathway. It has been demonstrated that naphthalene and phenanthrene share a common upper metabolic pathway (Kiyohara H, et al. 1994).
In addition, the metabolism of phenanthrene by Streptomyces flavovirens and the marine cyanobacterium Agmenellum quadruplicatum PR-6 is more similar to that reported in mammalian and fungal enzyme systems than those catalyzed by bacteria. Both oxidize phenanthrene to phenanthrene trans-9,10-dihydrodiol via a monooxygenase-epoxide hydrolase-catalyzed reaction rather than by a dioxygenase. The metabolic formation of 1-methoxyphenanthrene from phenanthrene was first reported in Synechococcus sp. PR-6. This organism may detoxify other 1-phenanthrols. The metabolic fate of 1-methoxyphenanthrene in Synechococcus sp. PR-6 remains to be elucidated.
Fungi also can metabolize phenanthrene by utilizing monooxygenases and epoxide hydrolases. The fungal metabolic pathways of phenanthrene (9S,10S) also involve oxidative attack at the "K-region" of phenanthrene.
The following is a text-format Phenanthrene 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.
Graphical Map (20k) Graphical Map (15k)
|----------------------------------------| |-----------------------------------------------------------------|
Phenanthrene Phenanthrene Phenanthrene
Aeromonas sp. s45p1 Marine Cyanobacterium Streptomyces flavovirens
Pseudomonas sp. Synechococcus sp. PR-6 |
s47p1,s7k5 | |
| | |
| +-- from the | |
| | Phenanthrene fungal| |
| | (9S,10S&9R,10R) | |
| | Pathway | |
| phenanthrene | | |
| dioxygenase | +---------------+---------------+ |
| | | | | |
v | | phenanthrene | | phenanthrene |
cis-3,4-Dihydroxy- | | 1,2- | | 9,10- |
3,4-dihydro- | | monooxygenase | | monooxygenase |
phenanthrene v v | v |
| [Phenanthrene- | [Phenanthrene- |
| 1,2-oxide] | 9,10-oxide] <--------+ |
| | | | | |
| cis-3,4- | | | | |
| dihydroxy- | | phenanthrene | phenanthrene- | |
| 3,4-dihydro- | rapid | 1,2- | 9,10- | |
| phenanthrene | isomerization | monooxygenase | epoxide | |
| dehydrogenase |(non-enzymatic)| | hydrolase | |
| | +----+ | | |
| | | v | |
from the v | | trans-9,10- | |
Pyrene Pathway --> 3,4-Dihydroxy- v | Dihydrodiol- | |
phenanthrene [1-Phenanthrol] <-+----------+ phenanthrene | |
| | | | |
| | | | |
| | +-------------------------+ |
| 3,4-dihydroxy- | 1-phenanthrol | +----------------+
| phenanthrene | methyltransferase | |
| dioxygenase | | | phenanthrene
| | | | 9,10-
| | | | monooxygenase
| v | | from the
| 1-Methoxy- | [Phenanthrene- -----> 9-Phenanthrol <--- Phenanthrene fungal
v phenanthrene +--> 9,10-oxide] A ^ (9S,10S&9R,10R)
2-Hydroxy-2H- | | | Pathway
benzo[h]chromene- | | |
2-carboxylate from the | phenanthrene- |
^ | Phenanthrene fungal | 9,10- |
| | 2-hydroxy-2H- (9S,10S&9R,10R) | epoxide | B
| | benzo[h]chromene- Pathway | hydrolase |
| | 2-carboxylate | |
| | isomerase | |
| v v |
trans-4- trans-9,10- |
(1'-Hydroxynaphth-2'-yl)- Dihydrodiol- -------------+
2-oxobut-3-enoate phenanthrene
|
| trans-4-
| (1'-hydroxynaphth-2'-yl)-
| 2-oxobut-3-enoate
| hydratase-aldolase
|
v
1-Hydroxy- + Pyruvate --------> Intermediary Metabolism (KEGG)
2-naphthaldehyde
|
|
| 1-hydroxy-
| 2-naphthaldehyde
| dehydrogenase
|
v
1-Hydroxy- only in Pseudomonas sp.
2-naphthoate --------------------+
| |
| |
| |
| 1-hydroxy- | 1-hydroxy-
| 2-naphthoate | 2-naphthoate
| 1,2-dioxygenase | hydroxylase
| |
| |
v v
trans-2'- 1,2-Dihydroxynaphthalene -------------> to the
Carboxy- Naphthalene Pathway
benzalpyruvate
|
|
| trans-2'-
| carboxy-
| benzalpyruvate
| aldolase
|
|
|
v
2-Carboxy- + Pyruvate -----> Intermediary Metabolism (KEGG)
benzaldehyde
|
| 2-carboxybenzaldehyde
| dehydrogenase
|
v
o-Phthalate
|
|
|
|
v
to the
Phthalate Pathway
Page Author(s): Jun Ouyang
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