Biotransformation of aromatic hydrocarbons

Varanasi, U., W.L. Reichert, J.E. Stein, D.W. Brown, and H.R. Sanborn. 1985. Bioavailability and biotransformation of aromatic hydrocarbons in benthic organisms exposed to sediment from an urban estuary. Environ. Sci. Technol. 19 836-841. 

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 ... 

MacGillivray AR, MP Shiaris (1993) Biotransformation of polycyclic aromatic hydrocarbons by yeasts isolated from coastal sediments. Appl Environ Microbiol 59 1613-1618. 

Warshawsky D, T Cody, M Radike, R Reilman, B Schumann, K LaDow, J Schneider (1995) Biotransformation of benzo[a]pyrene and other polycyclic aromatic hydrocarbons and heterocyclic analogues by several green algae and other algal species under gold and white light. Chem-Biol Interact 97 131-148. 

Allen CCR, DR Boyd, F Hempenstall, MJ Larkin, ND Sharma (1999) Contrasting effects of a nonionic surfactant on the biotransformation of polycyclic aromatic hydrocarbons to cw-dihydrodiols by soil hacierva.. Appl Environ Microbiol 65 1335-1339. 

Frank, A.P., Landrum, P.F., Eadie, B. J. (1986) Polycyclic aromatic hydrocarbon rates of uptake, depuration, and biotransformation by Lake Michigan Stylodrilus heringianus. Chemosphere 15, 317-330. 

This type of substrate-substrate interaction may be especially important for contaminants introduced as mixtures in the environment. One example is the mix of polycyclic aromatic hydrocarbons co-introduced in oil spills or in coal tar wastes. Laboratory observations of the biodegradation of such hydrocarbons show that some of these components can inhibit the removal of other compounds in the mix (Guha et al., 1999). Such results indicate that the rate of a particular chemical s biotransformation may be a function of factors such as the presence of competing substrates interacting with the same enzyme systems. 

By far the major portion of biotransformation is carried out in the liver by cytochrome P-450 (P-450), which is a collective term for a group of related enzymes or isoenzymes that are responsible for the oxidation of numerous drugs endogenous substances such as fatty acids, prostaglandins, steroids, and ketones and carcinogens such as polycyclic aromatic hydrocarbons, nitrosamines, hydrazines, and arylamines. 

The program is reported to carry out simple Hiickel molecular orbital calculations to determine the relative sensitivity of aromatic carbon atoms to oxidation and the relative stability of keto and enol tautomers. Klopman et al. (1999) have reported that for polycyclic aromatic hydrocarbons, adequate reactivity is an essential but not sufficient condition for enzyme catalyzed reaction. The accessibility of the reactive site (i.e., the absence of steric hindrance) was also found to be important. Genetic algorithms have been used to optimize the performance of the biotransformation dictionary by treating the initial priority scores set by expert assessment as adjustable parameters (Klopman et al., 1997). 

Fig. 3 Biotransformation of an aromatic hydrocarbon to an epoxide that undergoes various other reactions.

---