Metabolism of hydrocarbons

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 ... 

In early studies of the metabolism of hydrocarbons, it was noted that vicinal trans dihydrodiols were frequently found as hydrocarbon metabolites and, because of their trans configuration, Boyland... 

The amount of information on the microbial metabolism of hydrocarbons is much greater than the amount of information on the metabolism of organosulfur compounds (OSC). As work is progressing with studies on the latter group of compounds, results are showing that there are many similarities between the biodegradation pathways of OSC and those of hydrocarbons with similar structures. Therefore, included below is a short section describing some aspects of hydrocarbon metabolism. 

Petroleum contains a wide variety of OSC (13-17). However, in comparison to the amount of knowledge about the microbial metabolism of hydrocarbons, much less is known about the metabolism of OSC found in petroleum. These investigations have been hampered by the commercial unavailability of most of the sulfur compounds of interest. Because only a small number of OSC are available to workers studying microbial metabolism, few biodegradation pathways have been elucidated. 

Heider J., Spormann A. M., BelJer H. B., and Widdel E. (1999) Anaerobic bacterial metabolism of hydrocarbons. FEMS Microbiol. Rev. 22, 459-473. 

Aliphatic EC>8-EC16 Fraction. Hydrocarbons in this fraction are oxidatively metabolized to fatty acids and alcohols, apparently mediated by cytochrome P-450 isozymes (see Miller et al. 1996 for review). Studies regarding the metabolism of hydrocarbons in this fraction in humans or animals provide suggestive evidence that metabolism may be slow. In a study of humans exposed to 100 ppm white spirit 6 hours/day for 5 days (white spirit is a mixture comprised predominately of C10-C12 linear and branched alkanes), only minor differences were observed in the GC-MS spectrum of hydrocarbons in biopsied fatty tissue, than in the spectrum of hydrocarbons in the test material (Pedersen et al. 

Lee RF, Ryan C, Neuhauser ML (1976) Fate of petroleum hydrocarbons taken up from food and water by the blue crab Callinectes sapidus. Mar Biol 37 363-370 Lee RF, Furlong E, Singer S (1977) Metabolism of hydrocarbons in marine invertebrates aryl hydrocarbon hydroxylase from the tissues of the blue crab, Callinectes sapidus and the polychaete worm. Nereis sp. In Giam CS (1977) Pollutant effects on marine organisms. Lexington, Lexington, pp 111-124... 

Epoxides are often encountered in nature, both as intermediates in key biosynthetic pathways and as secondary metabolites. The selective epoxidation of squa-lene, resulting in 2,3-squalene oxide, for example, is the prelude to the remarkable olefin oligomerization cascade that creates the steroid nucleus [7]. Tetrahydrodiols, the ultimate products of metabolism of polycyclic aromatic hydrocarbons, bind to the nucleic acids of mammalian cells and are implicated in carcinogenesis [8], In organic synthesis, epoxides are invaluable building blocks for introduction of diverse functionality into the hydrocarbon backbone in a 1,2-fashion. It is therefore not surprising that chemistry of epoxides has received much attention [9]. 

Gibson DT, JR Koch, CL Schuld, RE Kallio (1968) Oxidative degradation of aromatic hydrocarbons by microorganisms. II. Metabolism of halogenated aromatic hydrocarbons. Biochemistry 7 3795-3802. 

Stirling LA, RJ Watkinson, IJ Higgins (1977) Microbial metabolism of alicyclic hydrocarbons isolation and properties of a cyclohexane-degrading bacterium. J Gen Microbiol 99 119-125. 

Cerniglia CE, JP Freeman, RK Mitchum (1982b) Glucuronide and sulfate conjugation in the fungal metabolism of aromatic hydrocarbons. Appl Environ Microbiol 43 1070-1075. 

Cerniglia CE, SA Crow (1981) Metabolism of aromatic hydrocarbons by yeasts. Arch Microbiol 129 9-13. 

Heitkamp MA, W Franklin, CE Cerniglia (1988b) Microbial metabolism of polycyclic aromatic hydrocarbons isolation and characterization of a pyrene-degrading bacterium. Appl Environ Microbiol 54 2549-2555. 

Kazunga C, MD Aitken (2000) Products from the incomplete metabolism of pyrene by polycyclic aromatic hydrocarbon-degrading bacteria. Appl Environ Microbiol 66 1917-1922. 

Whereas the metabolism of aromatic hydrocarbons takes place by dioxygenation, their biotransformation by yeasts and fungi is normally initiated by monooxygenation to the epoxide followed by hydrolysis to the trani-dihydrodiols. Phenols may subsequently be formed either by elimination or by nonenzymatic rearrangement of the epoxide ... 

Tsao C-W, H-G Song, R Bartha (1998) Metabolism of benzene, toluene, and xylene hydrocarbons in soil. Appl Environ Microbiol 64 4924-4929. 

Many process mixtures, notably fermentations, require sample preconcentration, microdialysis, microfiltration, or ultrafiltration prior to analysis. A capillary mixer has been used as a sample preparation and enrichment technique in microchromatography of polycyclic aromatic hydrocarbons in water.8 Microdialysis to remove protein has been coupled to reversed phase chromatography to follow the pharmacokinetics of the metabolism of acetaminophen into acetaminophen-4-O-sulfate and acetaminophen-4-O-glucu-ronide.9 On-line ultrafiltration was used in a process monitor for Aspergillus niger fermentation.10... 

Mineral Oil and Polyalphaolefin Hydraulic Fluids. No studies were located regarding metabolism in humans or animals after exposure to mineral oil hydraulic fluids or polyalphaolefin hydraulic fluids. It should be noted, however, that hydrocarbons found in mineral oils generally are not expected to undergo extensive metabolism in animals or humans (Cannon 1940 IARC 1984). It may be speculated that polyalphaolefins may undergo limited metabolism of a similar nature. 

In connection with the chemistry of the reactive transient species, nitrene, the chemistry of azepines is well documented u. Also, the chemistry of oxepins has been widely developed due to the recent interest in the valence isomerization between benzene oxide and oxepin and in the metabolism of aromatic hydrocarbons 2). In sharp contrast to these two heteropins, the chemistry of thiepins still remains an unexplored field because of the pronounced thermal instability of the thiepin ring due to ready sulfur extrusion. Although several thiepin derivatives annelated with aromatic ring(s) have been synthesized, the parent thiepin has never been characterized even as a transient species3). 

The developments which led to the present day concepts of the metabolic activation of hydrocarbons did not arise from the classical approach of identifying metabolites of greater biological potency than the parent compound, but from an approach dependent upon the assumption (or presumption) that the interaction of carcinogens with DNA is a key event in the initiation of the carcinogenic process. Brookes and Lawley (49) found in 1964 that when radioactive hydrocarbons are applied to the skin of mice, they become covalently bound to the DNA of the skin. Moreover, the extents of binding to DNA for various hydrocarbons followed fairly closely their relative carcinogenic activities. 

Figure 7. Steric model proposed by Jerina, et al. for the catalytic binding site of cytochrome P-450c (P-448) to account for the stereoselective metabolism of polycyclic aromatic hydrocarbons (48). The boundary should be enlarged in the directions shown to accommodate substrates whose mechanism of stereoselective oxygenation does not fit the steric model originally proposed.

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