Menthol is a monoterpene found in many essential oils, including spearmint and peppermint. It is widely used in commercial products such as toothpaste, mouthwashes, cigarettes, foods, and medicines (Gelal et al., 1999). In 1984, world production of this popular compound was estimated to be 3500 tons.
Thauera terpenica strain 21Mol is able to grow on (-)-menthol, as well as on (-)-menthone, (+)-isomenthol, (+)-isopulegol, and (+)-pulegone (Foss and Harder, 1998). Based on the bacterium's apparent requirement for an oxygen functional group at the C-3 atom, Hylemon and Harder (1998) suggest that the menthol degradation pathway resembles the anaerobic oxidation and cleavage of cyclohexanol described by Dangel et al. (1989). In this proposed pathway, menthol and the related substrates listed above are first converted to menth-2-enone, which is then oxidized to mentha-1,2-dione. This compound may then be attacked by HSCoA to produce 3,7-dimethyl-5-oxo-octyl-CoA, which in turn may be degraded on Seubert's pathway (Hylemon and Harder, 1998).
The following is a text-format menthol (anaerobic) 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 (9K) format.
(-)-(1R,2S,5R)-Menthol
Thauera terpenica strain 21Mol
|
|
| menthol
| dehydrogenase
|
v
(-)-(2S,5R)-Menthone
|
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| menthone
| dehydrogenase
|
v
(5R)-Menth-2-enone
|
|
| menth-2-enone
| hydratase
|
v
(5R)-3-Hydroxymenthone
|
|
| 3-hydroxymenthone
| dehydrogenase
|
v
Mentha-1,3-dione
|
|
| mentha-1,3-dione-
| CoA ligase
|
v
3,7-Dimethyl-5-oxo-octyl-CoA
|
|
| A
v
|
|
v
Carbon dioxide
Page Author(s): Andrew Vail and Carla Essenberg
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