Stereoselectivity of soman detoxication by organophosphorus acid anhydrases from Escherichia coli

Abstract

Three organophosphorus acid anhydrases have been isolated from E. coli by gel filtration and ion exchange column procedures, and further identified by gel electrophoresis. All three have molecular weights in the 120 000 – 140 000 range. Two of them hydrolyze racemic 1,2,2-trimethylpropylmethylphosphonofluoridate (soman) to completion at a single rate and, in parallel with this, detoxify soman at a comparable rate. The third enzyme appears to show stereoselectivity with respect to the two pairs of isomers of soman in that it hydrolyzes the racemic mixture at a fast and a slow rate, the latter approaching the non-enzymatic rate, and detoxifies soman only at the slower rate. In the past, organophosphorus acid anhydrases from bacterial and mammalian sources have been assayed either as crude sonicates or homogenates, or as cold ethanol precipitated fractions. Major discrepancies among laboratories have probably been due either to the assay of mixtures of varying proportions of these three enzymes depending on the various organs or organisms used as the source, or to the purification of one of the enzymes at the expense of the others. For E. coli, a fourth organophosphorus acid anhydrase is also present but at a considerably lower activity.