Purification and Properties of Soman-Hydrolyzing Enzyme from Human Liver

A soman-hydrolyzing enzyme (somanase) was purified from human liver. The human somanase is capable of hydrolyzing pinacolyl methylphosphonofluoridate (soman), diisopropylphosphorofluoridate (DFP), and ethyl-N-dimethyl phosphoramidocyanidate (Tabun) with P-F or P-CN bonding, but not ethyl (S-2-diisopropylaminoethyl) methylphosphonothiolate (VX) and diethyl-p-nitrophosphenylphosphate (paraoxon) with P-S or P-O bonding. The somanase has been purified 1570-fold with a specific activity of 41.4 μmol/min/mg protein. Its molecular weight is around 58 kDa determined by SDS-PAGE. The somanase could be stimulated by the divalent cations Mn⁺², Mg⁺², and Co⁺², where Co⁺² activation is the highest. The requirement of disulfide bonds for the enzyme activity was demonstrated by the inhibition effect of DTT.