Cycloalkane metabolism

Reviews on the microbial metabolism of hydrocarbons with biochemical aspects are available, and inclnde those of Britton (1984) on alkanes, and of Morgan and Watkinson (1994) that also includes cycloalkanes and some aromatic compounds. Virtually all the issues that are discussed in these recur in the examples that are used as illustration. Some broad generalizations are summarized ... 

As well as atmospheric sources, pyrolysis of fluorine-containing polymers, which may occur in engine oil additives, non-stick cookware or incinerated medical equipment (i.e. syringes) and household waste, may also produce TFA. This process may also produce perfluorinated alkanes and cycloalkanes, which have significant GWP, and have estimated tropospheric half-lives of more than 2000 years. Trifluoroacetate may also be produced by metabolism of trifluoromethyl-containing drugs such as Prozac, and anaesthetics including halothane and iso-fluorane [4],... 

The alkanes and cycloalkanes in diesel fuel are generally not readily metabolized, and are mostly excreted unchanged through the lungs, with a very small fraction excreted in the urine. The aromatic constituents of diesel are subject to oxidative metabolism and are typically excreted in the urine as water-soluble metabolites. 

In rats exposed by inhalation to single C6-CUI alkanes, cycloalkanes, or aromatic hydrocarbons at 100 ppm, 12 hours/day for 3 days, concentrations of alkanes and cycloalkanes were 2- to 3-fold higher than concentrations of aromatics 12 hours after cessation of exposure, suggesting that aliphatic hydrocarbons in this fraction may be metabolized more slowly than aromatic hydrocarbons of equivalent molecular weight (Zahlsen et al. 1992). 

Methane mooxygenase — and formally related systems — are involved in the bacterial hydroxylation of alkanes and cycloalkanes, and the epoxidation of alkenes. This has already been discussed in the context of Q-metabolism by bacteria (Section 4.3.2) and in greater detail in Chapter 6, Section 6.1.1. 

Some oil products are biologically quite easily metabolized, such as alkanes, alkenes, cycloalkanes and aromates. Products of this activity are differently oxidized oxygen derivatives (peroxides, alcohols, phenols, aldehydes, acids, etc.). In this way microorganisms enable self-cleaning processes in soil and rivers. The rate of these degradation reactions depends on sufficient access of oxygen from the air. 

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