Diisopropyl fluorophosphate nerve

The mechanism by which A-esterases hydrolyze organophosphates is not completely understood. Involvement of a phosphorylated active-site cysteine and displacement of an activated H20 molecule are two possible hypotheses (see Sect. 3.7.1) [56], A-Esterases comprise enzymes that hydrolyze aryl esters, paraoxon (2.2) and related organophosphate pesticides, and diisopropyl-fluorophosphate (DFP, diisopropyl phosphorofluoridate, 2.3) and related compounds, including nerve gases. These enzymes are found in the current nomenclature listed under arylesterases, aryldialkylphosphatase, and diisop-ropyl-fluorophosphatase. 

The serine proteases act by forming and hydrolyzing an ester on a serine residue. This was initially established using the nerve gas diisopropyl fluorophosphate, which inactivates serine proteases as well as acetylcholinesterase. It is a very potent inhibitor (it essentially binds in a 1 1 stoichiometry and thus can be used to titrate the active sites) and is extremely toxic in even low amounts. Careful acid or enzymatic hydrolysis (see Section 9.3.6.) of the inactivated enzyme yielded O-phosphoserine, and the serine was identified as residue 195 in the sequence. Chy-motrypsin acts on the compound cinnamoylimidazole, producing an acyl intermediate called cinnamoyl-enzyme which hydrolyzes slowly. This fact was exploited in an active-site titration (see Section 9.2.5.). Cinnamoyl-CT features a spectrum similar to that of the model compound O-cinnamoylserine, on denaturation of the enzyme in urea the spectrum was identical to that of O-acetylserine. Serine proteases act on both esters and amides. 

The nerve gas diisopropyl fluorophosphate (DFP) reacts with the serine —OH in some enzymes to form HF and the (9-phosphoryl ester as follows ... 

Clearly all experiments performed with the nerve gas, diisopropyl fluorophosphate (DFP), must be done in a fume hood with the utmost care. DFP rapidly hydrolyzes in 1 N NaOH, so that all glassware which comes in contact with the nerve gas should be soaked in this alkaline solution for at least 1 hr as a precaution prior to its reuse. (Warning DFP is a potent poison. Atropine is an effective antagonist. For details of treatment, see Goodman, L. S. and Gilman, A., 1965, The Pharmacological Basis of Therapeutics, The Macmillan Co., New York, 3rd Ed., p. 454). 

Wagner, G.W. and Bartram, P.W. 1999. Reactions of the nerve simulant diisopropyl fluorophosphate with selfdecontaminating adsorbents. A P MAS NMR Study. Journal of Molecular Catalysis A Chemical, 144 419 24. 

Uchiyama et al. (1987,1988a) immobilized squid nerve tissue in front of a fluoride ion sensitive electrode. The tissue contains diisopropyl fluorophosphatase, the activity of which was used to measure diisopropyl fluorophosphate. The sensor was stable for 18 days. 

Nerve agents also react with a tyrosine residue associated with the albumin fraction in blood (Black et al, 1999) (Figure 10). Analysis of tryptic digests from plasma incubated with sarin identified a phosphylated tripeptide, MeP(0)(0 Pr)-Tyr-Thr-Lys, consistent with the protein being albumin (tyrosine residue 411), although this sequence is common and occurs in other proteins. Before the advent of modern mass spectrometry, diisopropyl fluorophosphate was reported to... 

Acetylcholinesterase, the enzyme that catalyzes this hydrolysis, has a CH2OH group that is necessary for its catalytic activity. Diisopropyl fluorophosphate (DFP), a military nerve gas, inhibits acetylcholinesterase by reacting with the CH2OH group. 

Enzyme inhibitors are often poisonous. For example, diisopropyl-fluorophosphate is a nerve poison because the enzyme acetylcholinesterase has a reactive site serine. Chymotrypsin and acetylcholinesterase are both members of the class of enzymes known as serine esterases, which are all inhibited by diisopropylfluorophosphate. 

In a similar series of experiments, our laboratory demonstrated that topical exposure to a nerve agent stimulant, diisopropyl fluorophosphate (DFP), more than doubled permethrin absorption (Baynes etal., 2002). This significant effect on... 

Because of its high concentration in human plasma, BChE is also used as a biomarker for detection of exposure to OP pesticides and nerve agents. Hence, the sensor was likewise evaluated for detection of BChE-OP biomarkers. The detection method is the same as the protocol described previously in section 4.1 however, the chemical nerve agent (stracturally similar to Sarin) diisopropyl fluorophosphate (DFP) was chosen as a model OP in this studies. 

Such inhibition involves covalent bonding at the active site and cannot be reversed by excess substrate or by dialysis. The site is therefore blocked and made catalytically inactive. Most inhibitors in this group are highly toxic, e.g. the organophosphorus nerve poisons. Thus, diisopropyl fluorophosphate (DFP) reacts irreversibly with the hydroxyl group of serine ... 

The diisopropylfluorophosphatase (DFPase) is found in cephalopod nerve, hepatopancreas and saliva from squid (Anderson et al. 1988). Structurally similar to PONl, the DFPase also is a calcium-containing hydrolase with a six-bladed p-propeUer fold and readily hydrolysis the organophosphate fluoride, diisopropyl-fluorophosphate (DFP), as well as the nerve agents sarin, soman and cyclosarin, in addition to the cyanide-containing OP, the nerve agent tabun (Fig. 3.15). DFPase was initially found to hydrolyze P-F and P-CN bonds and to be inert toward P-0 or P-S bonds (Bigley and Raushel 2013). 

There have been descriptions of the acute effects in humans that follow high-dose exposure (>LDso) to nerve agents soman, sarin, and VX (Inoue, 1995 Nozaki et al., 1995 Nakajima et al., 1997). The similar cluster of behavioral symptoms (anxiety, psychomotor depression, intellectual impairment, and sleep disturbance) was observed in the immediate period after resolution of the acute signs of intoxication and then slowly faded with time, somehmes taking months to be fully resolved. The CNS symptoms noted after short-term exposure of humans to diisopropyl fluorophosphate (DFP) were... 

Insecticides and nerve gases act as irreversible inhibitors of acetylcholinesterase, an enzyme needed for nerve conduction. The compound DFP (diisopropyl fluorophosphate), an organophosphate insecticide, forms a covalent bond with the side chain —CH2OH of serine in the active site. When acetylcholinesterase is inhibited, the transmission of nerve impulses is blocked, and paralysis occurs. 

The A-esterases now classified as diisopropyl fluorophosphatases (diiso-propyl-fluorophosphate fluorohydrolase, DFPase, somanase, EC 3.1.8.2) were previously listed under EC 3.8.2.1. These enzymes, which hydrolyze P-F and P-CN bonds such as those of nerve gases, should be described as organophosphorus acid anhydrolases rather than phosphatases [56]. Diisopropyl-fluoro-phosphatases exist in different forms with contrasting substrate specificities. One form is able to hydrolyze paraoxon at a low rate, while others have no paraoxonase activity. The different forms differ in their molecular weights and in their requirements for bivalent cations for activity [56]. 

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