Biotransformation of xenobiotics

Examples of the Range of Plasmids Carrying Genes Coding Enzymes for the Biodegradation or Biotransformation of Xenobiotics... 

Parkinson, A. 1996. Biotransformation of xenobiotics. Chapter 6 in Casarett and Doull s Toxicology The Basic Science of Poisons. New York McGraw-Hill. 

Guengerich, F.P., "Pharmacogenomics of Cytochrome P450 and Other Enzymes Involved in Biotransformation of Xenobiotics," Drug Devel. Res., 49, 4-16 (2000). 

Data suggest that extrahepatic tissue (i.e., the immune system) may also play an important role in the in situ biotransformation of xenobiotics, such as polycyclic aromatic... 

Comparative Metabolism. Since the liver is the major organ involved in the biotransformation of xenobiotics, primary hepatocyte cultures provide an excellent model for in vitro metabolism studies. Primary hepatocyte cultures provide useful tools with which to study the comparative metabolism of xenobiotics by both humans and laboratory animals. 

Parkinson, A. (2001) The Biotransformation of Xenobiotics, in Casarett Boults Toxicology The Basic Science of Poisons, (ed. C.D. Klaasen), 5th edn., McGraw-Hill. 

One of the most intriguing and best explored specificities of hydrolases is their product enantiospecificity, a property that is not restricted to the biotransformation of xenobiotics since it is displayed by lipases acting on their physiological substrates. Indeed, prochiral triglycerides have been found to be hydrolyzed with marked product enantioselectivity by various lipases [51] [52], Such specificity can hardly be fortuitous and must have a physiological significance, which remains to be understood. 

A biological difference that could increase susceptibility of fetuses and premature or perinatal infants to 1,2-dibromoethane toxicity is developmental immaturity of the P-450 (microsomal enzyme) system. Biotransformation of xenobiotics occurs predominantly by glutathione conjugation (Benet and Sheiner 1985 Sipes and Gandolfi 1986). This pathway is known to generate a number of toxic intermediate metabolites of 1,2-dibromoethane. In addition, fetal mice have selective binding of... 

M.S. Benedetti, Biotransformation of xenobiotics by amine oxidases, Fundam. Clin. Pharmacol. 15 (2001) 75-84. 

The use of plant cells or enzymes extracted from the cells for the biotransformation of exogenous substances offers another method for producing flavours. This would be useful when compounds are not found in cell suspensions. Many studies have been carried out on the biotransformation of xenobiotics or pharmaceuticals by plant cell culture [43, 50]. 

Castagnoli, N. and Castagnoli, K.P. (1993) Biotransformation of xenobiotics to chemically reactive metabolites, in Drug Toxicokinetics. Drug and Chemical Toxicology Series vol. 9 (eds P.G. 

Klinger W. Biotransformation of xenobiotics during ontogenetic development. In Ruckpaul K, Rein H, eds. Frontiers of Bio transformation, Vol. II, Principles, Mechanisms and Biological Consequences of Induction. London Taylor Francis, 1990. 

Parkinson A. Biotransformation of Xenobiotics. In Klaassen CD, ed. Cassarett and DouII s Toxicology, The Basic Science of Toxicology. 6th ed. New York McGraw Hill, 2001. 

CYP1B1 is also expressed in the fetus in multiple tissues, particularly in thymus, spleen, kidney, and adrenal. A null CYP1B1 phenotype in humans has been associated with appearance of primary congenital glaucoma. Consistent with an important endogenous role for this enzyme in development of the eye, CYP1B1—which, in addition to biotransformation of xenobiotics, is also capable of metabolizing retinoid and sex steroids—is expressed in embryonic ocular tissues. 

Klaasson CD. 1986. Biotransformation of xenobiotics. In Cassarett Doull s Toxicology. 5th edihon, 113-120. 

Biotransformation of xenobiotics takes place in two phases. In phase I (= functionalization reactions), reactive groups are either activated or inserted into the substance molecule, thus providing the lipophilic molecule with a functional hydrophilic group. (In phase II, a hydrophilic residue is added to this group transferases hereby catalyze the conjugation with an endogenous substance.) Phase I elfects the insertion of reactive (polar) groups (such as -OH, -COOH, -SH, -NH2) by means of four chemical processes oxidation, reduction, hydrolysis, and hydration. 

In the course of cholestasis, lower concentrations of cytochrome P 450 are found together with increased activities of some microsomal oxidases. For this reason, the biotransformation of xenobiotics can be unpredictably and permanently altered. This is largely connected with the cholestasis-associated shift in bile acids from the periportal to the intermediary and perivenous zones. 

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