Benzo pyrene oxidation

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

Monooxygenase Assays. Incubation media contained the following (final concentrations) 0.05M phosphate buffer, pH 7.A, glucose-6-phosphate (G-6-P, 2.3 mM), G-6-P dehydrogenase (3 units), NADP (0.23 mM), and KC1 (2.8 mM), and various tissue preparations. Substrates were added in small volumes (25 yl or less) of MeOH. Samples (1.1 ml) were shaken in a thermostated (usually at 22°C) water bath and reactions terminated by enzyme denaturation. Specific analytical procedures for aldrin epoxi-dation (13), 1 CH30-p-nitroanisole 0-demethylation (1A), and 3H-benzo(a)pyrene oxidation (15) have been described. 

Benzo[a]pyrene in soot was the culprit for a large number of skin cancers in young boys who cleaned chimneys in the 1700s. The body transforms this compound to 4,5-benzo[a]pyrene oxide, a reactive epoxide that forms a covalent bond with DNA. 

L. L. Shipman, in Polynuclear Aromatic Hydrocarbons, R. Freudenthal and P. W. Jones, Eds., Raven Press, New York, 1976. Ab Initio Quantum Mechanical Characterization of the Ground Electronic State of Benzo[ ]pyrene. Implications for the Mechanism of Polynuclear Aromatic Hydrocarbon Oxidation to Epoxides by Cytochrome P-450. 

Figure 8 Schematic representation of binding interactions of aiene oxides at the H site of GST A, (4R,5S -benzo[a]pyrene oxide B, (5S,6R)-benzo[a]anthracene oxide C, (4R,5S)-pyiene oxide D, (7S)-styrene oxide, and E, (7R)-styrene oxide. (Taken from Dostal et al., 1986.)...

Figure 28 Glutathione conjugation reactions of aromatic and OC, P-unsatu-rated carbonyl compounds, benzo[a]pyrene oxide, and ethacrynic acid, respectively.

K. Inoue, and E.M.J. Gillam (2001). Specificity of I7p-oestradiol and benzo[a]pyrene oxidation by polymorphic human cytochrome P450 IBl variants substituted at residues 48, 119, and 432. Xenobiotica 31, 163—176. 

Benzo[a]pyrene-3,6-quinol and other quinols are involved in toxic quinone/quinol redox cycles (Lo-RENTZEN and Ts o 1977, Loeentzen etal. 1979). Quinols are formed from the corresponding qui-nones by several reductases. They are rapidly auto-xidizes while superoxide anions are formed. Benzo[fl]pyrene-3,6-quinone has been shown to be mutagenic in the Ames test, using tester strain TA 104 (Chesis et al. 1984) or TA 102, strains which are particularly sensitive to reactive oxygen species. In male Sprague-Dawley rats, a rapid increase of unmetabolised benzo[fl]pyrene was observed in sera 3h after benzo [a] pyrene treatment followed by a sharp decrease (Kim et al. 2000). The time-dependent pattern of serum lipid peroxidation and the level of erythrocyte antioxidant enzymes were shown to be related to the concentrations of the formation of benzo[ ]pyrene-quinones, oxidatively altered lipids and antioxidant enzymes in the blood. 

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

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