DDT dehydrochlorinase

DDT-dehydrochlorinase is an enzyme that occurs in both mammals and insects and has been studied most intensively in DDT-resistant houseflies. It catalyzes the dehydrochlorination of DDT to DDE and occurs in the soluble fraction of tissue homogenates. Although the reaction requires glutathione, it apparently serves in a catalytic role 

The diagram shows some reactions catalyzed by glutathione transferase that may give resistance to DDT or DDT analogues, methyl parathion but not the ethyl analogue, and lindane. 

Leukotriene A4 hydrolase is a unique cytosolic epoxide hydrolase, structurally dissimilar to the cytosolic enzyme described above. Its substrate specificity is narrow, being restricted to leukotriene A4, (5(S)-trans-5,6-oxido-7,9-cis-ll,l4-trans-eicosatetraenoic acid), and related fatty acids. 

In the early 1950s, it was demonstrated that DDT-resistant houseflies detoxified DDT mainly to its noninsecticidal metabolite DDE. The rate of dehydrohalogena-tion of DDT to DDE was found to vary between various insect strains as well as between individuals. The enzyme involved, DDT-dehydrochlorinase, also occurs in mammals but has been studied more intensively in insects. 

The lipoprotein enzyme has a molecular mass of 36,000 daltons as a monomer and 120,000 daltons as the tetramer. The Km for DDT is 5 x 10 7M with optimum activity at pH 7.4. This enzyme catalyzes the degradation of p,p-DDT to p,p-DDE or the degradation ofp,p-DDD (2,2,-bis(p-chlorophenyl)-l,l-dichloroethane) to the 

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Resistance to DDT has been developed in many insect species. Although there are some cases of metabolic resistance (e.g., strains high in DDT dehydrochlorinase activity), particular interest has been focused on kdr and super kdr mechanisms based upon aberrant forms of the sodium channel—the principal target for DDT. There are many examples of insects developing resistance to dieldrin. The best-known mechanism is the production of mutant forms of the target site (GABA receptor), which are insensitive to the insecticide. 

Lipke H, CW Kearns (1959a) DDT dehydrochlorinase I. Isolation, chemical properties, and spectrophoto-metric assay. J Biol Chem 234 2123-2128. 

Gooding et al. [9] used DDT-dehydrochlorinase for the identification of DDT in soils. The enzyme converts DDT to DDE which is then determined gas chromatographically on Chromosorb WHMDS at 190°C using an electron capture detector. 

The mercapturic acids and related compounds can then be exported from cells by an ATP-dependent export pump. Glutathione is a coenzyme for glyoxalase (Eq. 13-33), maleylacetoacetate isomerase (Eq. 13-20), and DDT dehydrochlorinase. The latter enzyme catalyzes elimination of HC1 from molecules of the insecticide and is especially active in DDT-resistant flies.3 Glutathione is said to be the specific factor eliciting the feeding reaction of Hydra that is, the release of glutathione from injured cells causes the little animal to engulf food. 

DDT dehydrochlorinase 551 Dead-end complexes 466 DEAE-cellulose 104 DEAE-Sephadex 106 Deamidation... 

Dehydrogenation A-Demethylation Hydroxylation Epoxidation Sulfoxidation Oxidations Acetaminophen, benzidine, DES, epinephrine Dimethylaniline, benzphetamine, aminocarb Benzo[a]pyrene, 2-aminofluorene, phenylbutazone 7,8-Dihydrobenzo[a]pyrene Methylphenylsulfide FANFT, ANFT, bilirubin Esterases and Amidases Paraoxon, dimethoate, phenyl acetate Epoxide Hydrolase Benzo(a)pyrene epoxide, styrene oxide DDT-Dehydrochlorinase p,p- DDT Glutathione Reductase Disulfiram... 

DDT-dehydrochlorinase, a reduced glutathione (GSH)-dependent enzyme, has been isolated from the 100,000g supernatant of resistant houseflies. Although the enzyme-mediated reaction requires glutathione, the glutathione levels are not altered at the end of the reaction (Figure 10.12). 

From the aforementioned findings, it is clear that insect cuticle contains various detoxification enzymes, including DDT-dehydrochlorinase, epoxide hydrolase, and cytochrome P450 monooxygenases. 

Clark, A.G. and Shamaan, N.A., Evidence that DDT-dehydrochlorinase from the house fly is a glutathione S-transferase, Pestic. Biochem. Physiol., 22, 249,1984. 

During the last two decades there has been continuing controversy concerning the classification of the enzyme DDT-dehydro-chlorinase as a GSH-S-transferase ( ). DDT-dehydrochlorinase is the enzyme that converts DDT to the relatively non-toxic DDE and has been intensively studied in houseflies and other insects because of its established importance in insect resistance to DDT. 

More recently DDT-dehydrochlorinase has been isolated and purified ( 660-fold) to apparent homogeneity from houseflies (49). In contrast to that described in earlier studies, this enzyme was found to be a dimer with subunits of molecular weights of 23,000 and 25,000. It was also found to possess substantial GSH-S-transferase activity towards 2,4-dinitrochlorobenzene and 3,4-dichloro-nitrobenzene. Based on its structure, catalytic activity and chromatographic behavior it was concluded that the purified heterodimeric DDT-dehydrochlorinase was indeed a GSH-S-transferase isozyme (49). It was proposed that instead of the nucleophilic substitution usually observed in GSH-S-transferase activity, DDT-dehydrochlorination by this enzyme involves an E2 elimination reaction in which the GS thiolate anion abstracts the hydrogen on the C-2 of DDT and this initiates the departure of the chlorine atom from C-1 ( 9) (Figure 9). 

DDT-dehydrochlorinase is a glutathione-dependent enzyme which is inhibited by chlorfenethol (Figure 2). It is linked to chromosome 2 of the house fly (4). 

Other ways of indicating the relationships and similarities of glutathione transferases have been used earlier. The first method, to classify them according to their activity, i.e., what they do, would have been much more useful for the toxicologist, but their substrate specificity is overlapping and there is a myriad of known and unknown possible substrates. A structural basis for classification is therefore more rational than a functional basis, such as the earlier terms aryl transferases, methyl transferases, epoxide transferases, DDT dehydrochlorinases, etc. 

The target biomolecules for DDT and the pyrethroids are the sodium channels in the axon. One very common type of resistance is the so-called knockdown resistance, or kdr resistance. In this case one or more amino acids have been changed due to point mutation so that DDT or pyrethroids do not bind. Whereas houseflies that are resistant due to the presence of the DDT dehydrochlorinase type of glutathione transferase will be paralyzed by DDT, it is found that when DDT has been detoxicated, the flies wake up and... 

After DDT dehydrochlorinase was found as one of the causes of DDT resistance in flies, it was subsequently found that N,N-dibutyl-p-chlorobenzene... 

Prapanthadara, L., Hemingway, ]., and Ketterman, A.J. 1995a. Ddt-resistance in Anopheles-gambiae (Diptera, Culicidae) from Zanzibar, Tanzania, based on increased Ddt-dehydrochlorinase activity of glutathione S-transferases. Bull. Entomol. Res., 85, 267-274. 

Summerford et al. (1951), March (1952) and Speroni (1952) showed that certain derivatives structurally related to DDT but inactive themselves can increase the effect of DDT on DDT-resistant flies. However, the same compounds are unable to enhance the effect on fly strains sensitive to DDT. These observations support the assumption that compounds known as DDT-synergists act by inhibiting the DDT-dehydrochlorinase enzyme. Various benzene sulfamide derivatives can also... 

DDT-dehydrochlorinase is only one of the enzymes causing detoxification of DDT. Also important in this respect are those mixed function oxydases which decrease the effect of DDT by inducing oxidative degradation. In his experiments carried out on Heliothis species, Plapp (1973) showed that the development of resistance to DDT can be traced back to oxidative enzymes. The field of action of these enzymes involves a wide range of insecticides. Accordingly, the effect of those anti-resistant compounds — the action of which is based on the inhibition of oxydases — is more general and concerns almost all types of insecticides. 

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