Nerve agents phosphylation

E. Elhanany, A. Ordentlich, O. Dgany, D. Kaplan, Y. Segall, R. Barak, B. Velan and A. Shafferman, Resolving pathways of interaction of covalent inhibitors with the active site of acetylcholinesterases MALDI-TOF/MS analysis of various nerve agent phosphyl adducts, Chem. Res. Toxicol., 14, 912-918 (2001). 

A major drawback of the fluoride reactivation method is that not all nerve agent adducts are amenable to fluoride reactivation, with the aged adduct of soman the best known example. This problem can be solved by looking at the BuChE enzyme itself Fidder et al (2002) published a method based on the LC-MS analysis of a nerve agent phosphylated nonapeptide derived after pepsin digestion of inhibited butyrylcholinesterase. The authors presented a procedure to extract BuChE from plasma using... 

Van der Schans, M.J., Polhuijs, M., Van Dijk, C., Degenhardt, C.E.A.M., Pleijsier, K., Langenberg, J.P., and Benschop, H.P. (2004). Retrospective detection of exposure to nerve agents analysis of phosphofluoridates originating from fluoride-induced reactivation of phosphylated BuChE. Arch. Toxicol., 78, 508-524. 

Williams, N.H., Harrison, J.M., Read, R.W., Black, R.M. (2007). Phosphylated tyrosine in alhumin as a hiomarker of exposure to organophosphorus nerve agents. Arch. Toxicol. 81 627-39. 

The recent study of Williams et al (2007) found that sarin, soman, cyclosarin, and tabun phosphylate a tyrosine residue on albumin in human blood. The tyrosine adducts with soman and tabun were detected in guinea pigs receiving therapy 7 days following subcutaneous administration of five times the LD50 dose of the respective nerve agent. VX also forms a tyrosine adduct in human blood in vitro but only at high concentrations. 

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... 

Phosphylation includes phophorylation and phosphonyla-tion, the latter being more common with nerve agents. 

The reversibility of inhibition is very important for carbamates. They react with AChE in the same manner, forming a carbamylated (inactive) enzyme, preventing phosphylation of the carbamylated portion of the enzyme however, spontaneous decarbamylation occurs very quickly and the released enzyme serves as a normal enzyme source, provided that no inhibitory concentration of an AChE inhibitor is present anymore. Therefore, reversible inhibitors (mostly carbamates) are used as prophylactics against OP/nerve agents intoxications. 

Read, R.W., Riches, J.R., Stevens, J.A., et al., 2010. Biomarkers of organophosphorus nerve agent exposure comparison of phosphylated butyrylcholinester-ase and phosphylated albumin after oxime therapy. Arch. Toxicol. 84, 25-36. Recommended Operating Procedures for Sampling and Analyses in the Verification of Chemical Disarmament. Rautio, M. (Ed.), 1994. The Ministry for Foreign Affairs of Finland, Helsinki. 

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