Phase II biotransformation

Glutathione S-transferase activity GST Phase II biotransformation enzyme PAHs, PCBs, OCPs, PCDDs Cytosol liver tissue (l.t.) 6-15... 

Dalvi RR. Alteration in hepatic phase I and phase II biotransformation enzymes by garlic oil in rats. Toxicol Lett 1992 60 299-305. 

McMahon, T.F., Beierschmitt, W.P., and Weiner, M., Changes in phase I and phase II biotransformation with age in male Fischer 344 rat colon Relationship to colon carcinogenesis, Cancer Lett., 36, 273,1987. 

Fish have active Phase I and Phase II biotransformation pathways that can modify the disposition and toxicity of pesticides. Although more studies are characterizing in vivo metabolites of pesticides in fish, there is still a significant lack of knowledge about the ultimate fate of these compounds in the fish. In addition, very little is known about the specific enzymes responsible for the formation of specific metabolites of various pesticides. For example, although multiple CYP isoforms have been identified in fish, the substrate specificities with regard to pesticides are unknown and deserve further study. 

The OSR includes induction of genes encoding Phase II biotransformation enzymes (GSTA, NQOl), enzymes involved in glutathione synthesis (y-glutamylcysteine synthase catalytic and regulatory subunits (y-GCS-c and y-GCS-r, respectively)),... 

Examples of Common Oxidation (Phase I) and Conjugation (Phase II) Biotransformations... 

Both phase I and phase II biotransformations are enzymatic reactions that normally take place in the liver. The type of phase I and phase II biotransformations, and the order and number in which they occur, are a function of the drug structure and available liver enzymes. A drug may undergo only phase 1 metabolism, or a phase I reaction with a subsequent phase II reaction. It is also possible for a drug to undergo the phase II reaction before undergoing the phase I and possibly a second phase II reaction, as well (e.g., the antituberculin drug isoniazid). 

Phase II biotransformation involves the enzymatic conjugation of a polar molecule to the drug molecule or to the phase I metabolite. These reactions include glucuronidation, acetylation, sulfation, or amidation. 

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