Microsomal benzo pyrene hydroxylase

Bend, J. R., Hall, P., and Foureman, G. L. Comparison of benzo(a)pyrene hydroxylase (aryl hydrocarbon hydroxylase, AHH) activities in hepatic microsomes from untreated and 1,2,3,4-dibenzanthracene (DBA)-induced little skate (Raja erinacea). Bull. Mt. Desert Island Biol. Lab. (1976) 16. 3-5. 

Wiebel, F. J., Leutz, J. C., Diamond, L., and Gelboin, H. V. Aryl hydrocarbon (benzo[a]pyrene) hydroxylase in microsomes from rat tissues differential inhibition and stimulation by benzoflavones and orqanic solvents. Arch. Biochem. Biophys. (1971) 144 78-86. 

Arylhydrocarbon (benzo[a]pyrene) hydroxylase, benzphetamine-N-demethylation, ethylmorphine-N-demethylation, ethoxycoumarin-0-deethylation and ethoxyresorufin-0-deethylation were performed by published procedures (31,32,33,34), but optimized for use with trout microsomes as described previously (30, 35). Hemoprotein P-450 was determined by the procedure of Estabrook et al. (36) to avoid spectral interference by hemoglobin. Microsomal protein content was estimated either by the method of Ross and Shatz (37) or Lowry et al. (38), using bovine serum albumin standards. 

Initial studies designed to obtain a valid subcellular fractionation scheme for rainbow trout liver illustrated the aryl-hydrocarbon (benzo[a]pyrene] hydroxylase activity separated with glucose-6-phosphatase (35). This observation indicated that the trout hemoprotein P-450-mediated monooxygenation system was located within the endoplasmic reticulum (microsomal fraction). 

Ghosh, D. K., Dutta, D., Samanta, T. B. Mishra, A. K. (1983). Microsomal benzo[a]pyrene hydroxylase in Aspergillus ochraceus TS Assay and characterization of the enzyme system. Biochemistry and Biophysics Research Communications, 113, 497-505. 

Ethynylpyrene, a suicide inhibitor of cytochrome P-450 dependent benzo[a]pyrene hydroxylase activity in liver microsomes. Biochemistry 23, 3827-3836. 

Gan, L.-S.L, A.L. Acebo, and W.L. Alworth (1984). 1-Ethynylpyrene, a suicide inhibitor of cytochrome P-450 dependent benzo(a)pyrene hydroxylase activity in liver microsomes. Biochemistry 23, 3827-3836. 

Figure 9.1. Sex-differences in rat hepatic microsomal drug metabolism. Data shown are based on enzyme assays in rat liver microsomes using the three indicated xenobiotic substrates ethylmorphine (EM), benzo[o] pyrene (BP), and hexobarbital (HB). Ethylmorphine A -demethylase and benzo[a]pyrene hydroxylase activities are expressed as nmol product formed per minute per mg microsomal protein, whereas hexobarbital hydroxylase activity is expressed as nmol product formed per 30 min per g liver. Also shown is hepatic microsomal total cytochrome P450 content, which is expressed as nmol per mg microsomal protein (values multiplied by 10). The data are shown as mean SD for 4 or 5 rats, except for ethylmorphine W-demethylase and total P450 which are based on a pool of 6 livers.

Characteristics of chemicals showing high transfer from maternal blood to placenta include low molecular weight (< 500 daltons optimal), high lipid/water partition coefficient (lipophilic), low ionization at blood pH (pKa) and low binding to plasma proteins ( ). The placenta contains a full complement of mixed function oxidases located in the microsomal and mitochondrial subcellular fractions capable of induction (eg. benzo(a)-pyrene hydroxylase, 24). 

Benzo(a)pyrene hydroxylase activities in hepatic and intestinal microsomes of fiber-fed rats are presented in Table VIII. There were no significant differences (0.05 level) among any of the purified fiber treatment groups in either liver or intestinal microsomes. Lab Chow-fed rats had the lowest liver microsomal benzo(a)pyrene hydroxylase (AHH) level. The indication of enhanced intestinal P-448-dependent hydroxylation of biphenyl in the pectin-fed rats (seen as elevated 3-hydroxybiphenyl formation in microsomes, Table Vl) was not supported by these preliminary data. 

Table 14. Responses of microsomal cytochrome P-450, NADPH-cytochrome c (P-450) reductase and benzo[a]pyrene hydroxylase activities (radiometric and fluorometric) to experimental exposure of molluscs to xenobiotics ... 

No studies were located regarding the metabolic pathway of fuel oils in humans. In one animal study, fuel oil no. 2 applied to the skin of rats induced cutaneous aryl hydrocarbon hydroxylase activity in rat skin microsomal preparations by causing a three-fold induction of benzo(a)pyrene (BaP) 3-hydroxylase activity (Rahimtula et al. 1982). In addition, BaP 3-hydroxylase activity was selectively inhibited by -naphthoflavone, but not by metyrapone, suggesting that cytochrome P-448 enzymes are induced and may participate in the metabolism of this fuel oil (Rahimtula et al. 1982). 

Aryl hydrocarbon hydroxylase (AHH) is part of the microsomal mixed-function oxidase system involved in the detoxification of polycyclic aromatic hydrocarbons. In the HPLC assay developed for the AHH activity, benzo[a]pyrene (BaP) is used as the substrate, and the activity is determined by measuring the unreacted BaP during the reaction. 

Rats were dosed with soil suspensions, by gavage, either once or for four consecutive days. Total TCDD dosages administered to rats were either 10 ug TCDD/kg or 40 ug/ TCDD/kg. Rats were sacrificed 24 hours after the final dose, autopsied, and hepatic microsomal fractions were collected. Aryl hydrocarbon hydroxylase (AHH) levels were determined in the microsomes, using the fluorescent assay of the product of the metabolism of benzo(a)pyrene to 3-OH benzo(a)pyrene (16). 

Addition of chromium(VI) to homogenates containing the microsomal fraction of rat lung tissue dramatically inhibited the benzo[a]pyrene (BP) hydroxylase actmty known to... 

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