Diisopropyl fluorophosphatase

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]. 

Phosphatases are numerous and important enzymes (see also Chapt. 2). They are classified as phosphoric monoester hydrolases (phosphatases, EC 3.1.3), phosphoric diester hydrolases (phosphodiesterases, EC 3.1.4), triphosphoric monoester hydrolases (EC 3.1.5), diphosphoric monoester hydrolases (pyrophosphatases, EC 3.1.7), and phosphoric triester hydrolases (EC 3.1.8) [21] [63]. Most of these enzymes have a narrow substrate specificity restricted to endogenous compounds. However, some of these enzymes are active toward xenobiotic organophosphorus compounds, e.g., alkaline phosphatase (EC 3.1.3.1), acid phosphatase (EC 3.1.3.2), aryldialkylphosphatase (para-oxonase (PON1), EC 3.1.8.1) and diisopropyl-fluorophosphatase (tabunase, somanase, EC 3.1.8.2) [64 - 70]. However, such a classification is far from definitive and will evolve with further biochemical findings. Thus, a good correlation has been found in human blood samples between somanase and sarinase activities on the one hand, and paraoxonase (PON1) type Q isozyme concentrations on the other [71]. 

As anhydrides, such compounds are subject to spontaneous hydrolysis, which may contribute to detoxification [160]. Thus, soman hydrolysis at pH 7.5 and 37° occurs with a rate constant of 0.003 - 0.004 min-1 and an activation energy of ca. 55 kJ mol 1 [161]. However, most of the published data refer to enzymatic hydrolysis. Enzymes hydrolyzing P-X anhydride bonds are now known as organophosphorus acid anhydrolases (OPA anhydrolases) classified as EC 3.1.8.2 (also known as diisopropyl-fluorophosphatase, DFPase, tabunase, somanase), an activity related to EC 3.1.8.1 (aryldialkyl-phosphatase, paraoxonase, A-esterase) and formerly classified as EC 3.8.2.1 [64] [65] [69], Much public information on these enzymes can be found in [106],... 

Hartleib, J., Ruteijans, H. (2001). High-yield expression, purification, and characterization of the recombinant diisopropyl-fluorophosphatase from Loligo vulgaris. Protein Expr. Purif. 21 210-19. 

Blum, M.M., Timperley, C.M., Williams, G.R., Thiermann, H., Worek, F. (2008). Inhibitory Potency against human acetylcholinesterase and enzymatic hydrolysis of fluorogenic nerve agent mimics by human paraoxonase 1 and squid diisopropyl fluorophosphatase. Biochemistry 47(18) 5216-24. 

Hartlieb, J., Rilterjans, H. (2001). Insights into the reaction mechanism of the diisopropyl-fluorophosphatase Jrom Loligo vulgaris by means of kinetic studies, chemical modification and site-directed mutagenesis. Biochim. Biophys. Acta 1546 312-24. 

EC 3.1.8 Phosphoric triester hydrolases EC 3.1.8.1 Paraoxonase (PON) PONl, PON2, PON3 EC 3.1.8.2 Diisopropyl-fluorophosphatase... 

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. 

Blum, MM., Lohr, F., Richard A., et al, 2006. Binding of a designed substrate analogue to diisopropyl fluorophosphatase implications for the phosphot-riesterase mechanism. J. Am. Chem. Soc. 128,12750-12757. 

Scharff, E.I., Koepke, J., Fritzsch, G., et al., 2001. Crystal structure of diisopropyl-fluorophosphatase from Loligo vulgaris. Structure 9 (6), 493-502. 

Belinskaya, T, Pattabiraman, N., diTargiani, R., et al, 2012. Differences in amino acid residues in the binding pockets dictate substrate specificities of mouse senescence marker protein-30, human paraoxonase 1, and squid diisopropyl-fluorophosphatase. Biochim. Biophys. Acta 1824, 701-710. 

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