ENZYMATIC-HYDROLYSIS OF THE CHEMICAL WARFARE AGENT-VX AND ITS NEUROTOXIC ANALOGS BY ORGANOPHOSPHORUS HYDROLASE

Organophosphorus hydrolase (OPH) is a bacterial enzyme that hydrolyzes a variety of organophosphorus (OP) neurotoxins, including many widely used pesticides and chemical warfare agents containing P-O, P-F, P-CN and P-S bonds. It has extremely high efficiency in hydrolysis of many different phosphotriester and phosphothiolester pesticides (P-O bond) such as paraoxon (k(cat) > 3800 s(-1)) and coumaphos (k(cat) = 800 s( -1)) or phosphonate (P-F) neurotoxins such as DFP (k(cat) = 350 s(-1)) and the chemical warfare agent sarin (k(cat) = 56 s(-1)). In contrast , the enzyme has much lower catalytic capabilities for phosphonothioat e neurotoxins such as acephate (k(cat) = 2.8 s(-1)) or the chemical wa rfare agent VX [O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothi oate] (k(cat) = 0.3 s(-1)). This lower specificity for VX and its anal ogues are reflected by the specificity constants (k(cat)/K-m values) f or VX = 0.75 x 10(3) M-1 s(-1) compared to 5.5 x 10(7) M-1 s(-1) for p araoxon. Different metal-associated forms of the enzyme demonstrated s ignificantly varying hydrolytic capabilities for VX and its analogues, and the activity of OPH (Co+2) was consistently higher than that of O PH (Zn+2) by five to twenty fold. Hydrolysis of the P-S bonds was dete rmined by monitoring the formation of free -SH groups, and the specifi c cleavage of the P-S bond was verified by P-31 NMR analysis.