Diisopropyl fluorophosphate model

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. 

Wagner-Jauregg, T., Hackley Jr., B.E., Lies, T.A., Owens, O.O., and Proper, R. 1955. Model reactions of phosphoms-containing enzyme inactivators. IV. The catal)Tic activity of certain metal salts and chelates in the hydrolysis of diisopropyl fluorophosphate. Journal of the American Chemical Society, 77 922-929. 

Gearhart, J.M., Jepson, G.W., Clewell, H.J., Andersen, M.E., and Conolly, R.B., Physiologically based pharmacokinetics and the pharmacodynamic model for inhibition of acetylcholinesterase by diisopropyl fluorophosphate, Toxicol. Appl. Pharmacol., 106, 295, 1990. 

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. 

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