Detoxification enzymes regulation

A CA epoxidase perhaps identical to the precocene epoxidase biosynthesizes Insect juvenile hormones (JH) from the analogous inactive oleflnic precursor, and the enzyme activity appears higher in precocene-sensitive species (32). Subsequent detoxification of JH occurs primarily by EHs and esterases in peripheral tissues, and preliminary information does not indicate major differences for JH degradation routes between chewing and sucking herbivores, or insect carnivores (33,34). More study of the role of detoxification in regulating the action of JH in target tissues is required. 

The expression of proteins involved in Hg(II) detoxification is regulated by the MerR protein. The MerR protein is always bound as a dimer adjacent to the RNA polymerase binding site of the mer gene. In the absence of Hg, MerR holds the DNA in a conformation so that the RNA polymerase binding is blocked and transcription cannot occur. When the mercury binds to MerR, it changes the conformation of the MerR protein-DNA complex and allows RNA polymerase to bind and transcribe the mer operon, creating mRNA for the series of enzymes that carry out mercury resistance. 

Calmodulin, a calcium binding protein, is involved in Ca2+-dependent regulation of several synaptic functions of the brain synthesis, uptake and release of neurotransmitters, protein phosphorylation and Ca+2 transport. It reacts with TET, TMT and TBT which then inactivates enzymes like Ca+2-ATPase and phosphodiesterase. In vitro studies indicated TBT was greater at inhibiting calmodulin activity than TET and TMT, whereas in vivo the order was TET > TMT > TBT. This may be due to the greater detoxification of TBT (66%) in the liver before moving to other organs30,31. 

There is no information on the metabolism of 3,3 -dichlorobenzidine in children. Limited data in humans suggest that N-acetylation is an important metabolic pathway (Belman et al. 1968), and a detoxification mechanism. N-Acetylation in humans is likely done by one of two families of N-acetyltransferases. One of these families, NAT2, is developmentally regulated (Leeder and Kearns 1997). Some enzyme activity can be detected in the fetus by the end of the first trimester. Almost all infants exhibit the slow acetylator phenotype between birth and 2 months of age. The adult phenotype distribution is reached by the age of 4-6 months, whereas adult activity is found by approximately 1-3 years of age. Also, UDP-glucurono-syltransferase, responsible for the formation of glucuronide conjugates, seems to achieve adult activity by 618 months of age (Leeder and Kearns 1997). These data suggest that metabolism of 3,3 -dichloro-benzidine by infants will differ from that in adults in extent, rate, or both. 

It is possible that these ecoregulatory enzymes, used by the insect to inhibit targeted plant toxlficatlon systems, may themselves be the principal target of the production of tannins by plants. The discovery of other examples of secondary chemical interactions with enzymes dedicated to the regulation of toxifica-tion and detoxification mechanisms may be expected as our knowledge of chemically mediated plant-insect interaction expands. 

Peroxiredoxins Group of antioxidant thioredoxin-dependent enzymes with a catalytic fnnc-tion in the detoxification of cellnlar-toxic peroxides. See Claiborne, A., Ross, R.P., and Parsonage, D., Flavin-linked peroxide rednctases protein-sulfenic acids and the oxidative stress response. Trends Biochem. Sci. 17, 183-186, 1992 Dietz, K-J., Horhing, R, Konig, J., and Baien, M., The function of chloroplast 2-cysteine peroxiredoxin I peroxide detoxification and its regulation, J. Expt. Bot. 53, 1321-1329, 2002 Immenschuh, S. 

Recently, it has been found that, in addition to its detoxification function and its function as a biomarker for up-regulation of other phase II enzymes, up-regulation of quinone reductase by monofunctional inducers may play a role in the stabilization of p53, the protein product of a tumor suppressor gene, which induces growth arrest and apoptosis. Sulforaphane has also been shown to mediate growth arrest and induce cell cycle arrest and apoptosis in many cancer cell lines, including those of human prostate, colon, and T-cell leukemia origin. - The exact mechanisms, and whether all the bioactivities of sulforaphane involve the ARE, are not yet understood. 

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