Enzyme insects

Johnston, K.A., Fee, M., Brough, C., Hilder, V.A., Gatehouse, A.M.R. and Gatehouse, J.A. (1995). Protease activities in the larval midgut of Heliothis virescens Evidence for trypsin and chymotrypsin-like enzymes. Insect Biochem. Mol. Biol. 25,375-383. 

Roditakis E, Morou E, Tsagkarakou A, Riga M, Nauen R, Paine M, Morin S, Vontas J (2011) Assessment of the Bemisia tabaci CYP6CMlvQ transcript and protein levels in laboratory and field-derived imidacloprid-resistant insects and crossmetabolism potential of the recombinant enzyme. Insect Sci 18 23-29... 

A few cyanohydrins and ethers of cyanohydrins occur naturally One species of millipede stores benzaldehyde cyanohydrin along with an enzyme that catalyzes its cleavage to benzaldehyde and hydrogen cyanide m separate compartments above its legs When attacked the insect ejects a mixture of the cyanohydrin and the enzyme repelling the invader by spraying it with hydrogen cyanide... 

The development of malathion in 1950 was an important milestone in the emergence of selective insecticides. Malathion is from one-half to one-twentieth as toxic to insects as parathion but is only about one two-hundredths as toxic to mammals. Its worldwide usage in quantities of thousands of metric tons in the home, garden, field, orchard, woodland, on animals, and in pubHc health programs has demonstrated substantial safety coupled with pest control effectiveness. The biochemical basis for the selectivity of malathion is its rapid detoxication in the mammalian Hver, but not in the insect, through the attack of carboxyesterase enzymes on the aUphatic ester moieties of the molecule. 

Mode of Action. All of the insecticidal carbamates are cholinergic, and poisoned insects and mammals exhibit violent convulsions and other neuromuscular disturbances. The insecticides are strong carbamylating inhibitors of acetylcholinesterase and may also have a direct action on the acetylcholine receptors because of their pronounced stmctural resemblance to acetylcholine. The overall mechanism for carbamate interaction with acetylcholinesterase is analogous to the normal three-step hydrolysis of acetylcholine however, is much slower than with the acetylated enzyme. 

It is commercially prepared from benzaldehyde and hydrogen cyanide. Mandelonitrile is used by certain insects (tiger beedes, an African millipede) as a defense duid (38). After expelling the duid an enzyme catalyzes the conversion of mandelonitrile to benzaldehyde and HCN, which is usually fatal to the insect s enemy. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Bacillus thuringiensis produces a variety of organic compounds which are toxic to the larvae of certain susceptible insect hosts. Among the toxic entities are proteinaceous crystals, probably three soluble toxins, and certain enzymes. The protein material is the major toxin active in killing lepidopterous larvae. The protein is formed by the cells apparently in close synchrony with sporulation, and its nature is a constant function of bacterial strain. The mode of action of the protein is under study. The sequence of events in the pathology observed is probably solubilization of the crystal (enzymatic or physical)—>liberation of toxic unit—>alteration of permeability of larval gut wall— change in hemolymph pH—>invasion of hemolymph by spores or vegetative cells of the bacterium. 

Methyl parathion can enter your body if you eat food or drink water containing it if you swim, bathe, or shower in contaminated water if you touch recently sprayed plants or soil if you touch contaminated soil near hazardous waste sites or if you breathe air that contains methyl parathion, such as near factories or recently sprayed farm fields (or in recent accounts of the illegal use of methyl parathion, if you breathe air or touch contaminated surfaces inside homes where methyl parathion has been used to kill insects). By any means of exposure, methyl parathion goes into your body quickly and gets into your blood. From your bloodstream, methyl parathion goes to your liver, brain, and other organs. Your liver changes some of methyl parathion to a more harmful chemical called methyl paraoxon. Both methyl parathion and methyl paraoxon can bind to enzymes of your nerves within minutes or hours. Your liver breaks down methyl parathion and methyl paraoxon into less harmful substances. These less harmful substances leave your body in urine within hours or days. For more information, see Chapter 3. 

Stumpf JL. Shehab N. Patel AC Safety of angiotensin-converting enzyme inhibitors in patients with insect venom allergies. Ann Pharmacother 2006 40 699-703. 

This is the first example of a reaction for which the presence of a chelating ligand was observed to facilitate rather than retard metal-catalysed epoxidation (Gao et al., 1987). It was found that the use of molecular sieves greatly improves this process by removing minute amounts of water present in the reaction medium. Water was found to deactivate the catalyst. All these developments led to an improved catalytic version that allows a five-fold increased substrate concentration relative to the stoichiometric method. Sensitive water-soluble, optically active glycidols can be prepared in an efficient manner by an in situ derivatisation. This epoxidation method appears to be competitive with enzyme-catalysed processes and was applied in 1981 for the commercial production of the gypsy moth pheromone, (-1-) disparlure, used for insect control (Eqn. (25)). 

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