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Human serum paraoxonase 1 (HuPON1; EC 3.1.8.1) is a calcium-depend-ent six-foldb-propeller enzyme that has been shown to hydrolyze an array of substrates, including organophosphorus (OP) chemical warfare nerve agents. Although recent efforts utilizing site-directed mutagenesis have demonstrated specific residues (such as Phe222 and His115) to be import- | ỊFEBS Journal Direct detection of stereospecific soman hydrolysis by wild-type human serum paraoxonase David T. Yeung1 2 J. Richard Smith3 Richard E. Sweeney4 David E. Lenz1 and Douglas M. Cerasoli1 1 Physiology and Immunology Branch Research Division US Army MedicalResearch Institute of ChemicalDefense Aberdeen Proving Ground MD USA 2 Department of Pharmacology and ExperimentalTherapeutics University of Maryland at Baltimore MD USA 3 MedicalDiagnostic and ChemicalBranch AnalyticalToxicology Division US Army MedicalResearch Institute of ChemicalDefense Aberdeen Proving Ground MD USA 4 RESECO Research Engineering Consultants Nottingham PA USA Keywords diisopropylfluorophosphate GC MS paraoxonase 1 soman stereoselectivity Correspondence D. Cerasoli US Army MedicalResearch Institute of ChemicalDefense 3100 Ricketts Point Road Aberdeen Proving Ground MD 21010-5400 USA Fax 1 410 436 8377 Tel 1 410 436 1338 E-mail douglas.cerasoli@us.army.mil Received 19 October 2006 revised 5 December 2006 accepted 13 December 2006 doi 10.1111 j.1742-4658.2006.05650.x Human serum paraoxonase 1 HuPONl EC 3.1.8.1 is a calcium-dependent six-fold b-propeller enzyme that has been shown to hydrolyze an array of substrates including organophosphorus OP chemical warfare nerve agents. Although recent efforts utilizing site-directed mutagenesis have demonstrated specific residues such as Phe222 and His115 to be important in determining the specificity of OP substrate binding and hydrolysis little effort has focused on the substrate stereospecificity of the enzyme different stereoisomers of OPs can differ in their toxicity by several orders of magnitude. For example the C P- isomers of the chemical warfare agent soman GD are known to be more toxic by three orders of magnitude. In this study the catalytic activity of HuPON1 towards each of the four chiral isomers of GD was measured simultaneously via chiral GC MS. The catalytic efficiency kcat Km of the wild-type enzyme for the various .
