Citronellol is a linear terpene that occurs naturally in citrus plants. It is used commercially as a flavor and odor agent in perfumes, cosmetics, detergents, household cleaners, “biosafe” insect repellents, and various food products. Citronellol does not present any known health risks to humans (Hoschle et al., 2005).
Degradation of citronellol in Pseudomonas citronellolis, Pseudomonas mendocina, and Pseudomonas aeruginosa begins with oxidation of the alcohol and formation of the CoA ester which is converted to cis-geranyl-CoA. Linear terpenes, such as citronellol and geraniol, contain beta-methyl groups that inhibit beta-oxidation (Cantwell et al., 1978). A key enzyme (geranyl-CoA carboxylase) in the degradation of these compounds converts the beta-methyl group to an acetate. The carboxylated intermediate undergoes hydratization and the actetate side group is eliminated by 3-hydroxy-3-isohexenylglutaryl-CoA lyase. The 7-methyl-3-oxo-ocanoyl-CoA product is readily assimilated via beta-oxidation. 3-Methylcrotonyl-CoA is likely degraded via the leucine degradation pathway (Aquilar et al., 2006). Due to structural similarities between citronellol and geraniol, it is assumed that the oxidation of these compounds is catalyzed by the same enzymes (Cantwell et al., 1978).
The following is a text-format Citronellol degradation pathway map. Organisms that can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on specific compounds or reactions. This map is also available in graphic (19k) format.
Citronellol Pseudomonas aeruginosa Pseudomonas citronellolis Pseudomonas mendocina | | citronellol dehydrogenase | v Citronellal | | citronellal dehydrogenase | v Citronellate | | citronellyl-CoA ligase | v Citronellyl-CoA | | | citronellyl-CoA | dehydrogenase | v from the cis-Geranyl-CoA <------------- Geraniol Pathway | | geranyl-CoA carboxylase | v Isohexenylglutaconyl-CoA | | isohexenyl- | glutaconyl-CoA hydratase | v 3-Hydroxy- 3-isohexeneylglutaryl-CoA | | 3-hydroxy- | 3-isohexenylglutaryl-CoA | acetate lyase | v 7-Methyl-3-oxo-6-octenoyl-CoA + Acetate | | | acetoacetyl-CoA thiolase | v 5-Methylhex-4-enoyl-CoA + Acetyl-CoA | | | adipyl-CoA dehydrogenase | v (2E)-5-Methylhexa-2,4-adienoyl-CoA | | | enoyl-CoA hydratase | v 3-Hydroxy-5-methylhex-4-enoyl-CoA | | 3-hydroxyacyl-CoA | dehydrogenase | v 5-Methyl-3-oxo-4-hexenoyl-CoA | | | acetoacetyl-CoA thiolase | v 3-Methylcrotonyl-CoA + Acetyl-CoA | | | | | | v v Intermediary Intermediary Metabolism Metabolism (KEGG) (KEGG)
Page Author(s): Dean G. Binger, Michael Turnbull
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