n-Octane is used in organic syntheses, calibrations, and azeotropic distillations and is a common component of gasoline and other petroleum products. The engine fuel antiknocking properties of an isomer of n-octane (2,2,4-trimethylpentane or isooctane) are used as a comparative standard in the Octane Rating System.
Many microorganisms, including several Pseudomonads, are able to use linear alkanes as their sole source of carbon and energy (Beilen et al., 1994). The OCT-plasmid of Pseudomonas oleovorans contains two operons, alkBFGHJKL and alkST, which encode all proteins necessary for the degradation of n-octane and other five- to twelve-carbon linear alkanes (Beilen et al., 1994). Branched isomers, such as isooctane, are less susceptible to biodegradation than n-octane (Schaeffer et al., 1979).
The conversion of n-octane to 1-octanol is catalyzed by a group of proteins collectively referred to as the "alkane hydroxylase system." It has three main components: alkane 1-monooxygenase, and the two soluble proteins rubredoxin, and rubredoxin reductase. Rubredoxin reductase transfers electrons from NADH to rubredoxin. This protein then passes electrons to alkane 1-monoxygenase, an enzyme localized in the cytoplasmic membrane. The final product of this pathway, octanoyl-CoA, enters the beta-oxidation cycle and is used as both a carbon and energy source (Beilen et al., 1994). The alkyl hydroperoxide reductase enzyme system of Salmonella choleraesuis (formerly S. typhimurium) is composed of two enzymes (AhpC and AhpF) which reduce organic hydroperoxides and hydrogen peroxide (Poole 1996. Homologs of these enzymes are found in a variety of Gram-positive and Gram-negative species.
The following is a text-format n-octane degradation 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 (7k) format.
n-Octane
Pseudomonas oleovorans
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| alkane 1-monooxygenase
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v
1-Octanol <------------------------ Octane hydroperoxide
| alkyl hydroperoxide Salmonella choleraesuis
| reductase
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| alcohol dehydrogenase
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v
1-Octanal
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| aldehyde dehydrogenase
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v
Octanoate
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| acyl-CoA synthetase
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v
Octanoyl-CoA
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v
Intermediary
Metabolism
(KEGG)
Page Author(s): David Wills, Stephen Stephens and Edward Bryan
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