Organophosphorus acid anhydrolase in slime mold duckweed and mung bean: a continuing search for a physiological role and a natural substrate

Recently, and for the first time, a diisopropylphosphorofluoridate (DFP)-hy drolyzing enzyme, i.e. an organophosphonus acid anhydrolase (OPAA), has bee n reported in a plant-source. Based on this and other suggestive evidence, the ability of three plant sources and a protist to hydrolyze DFP and 1,2,2 -trimethylpropyl methylphosphonofluoridate (Soman) were tested, and the eff ects of Mn2+ and ethylenediamine tetraacetate (EDTA) on this activity. The plants are duckweed (Lemna minor), giant duckweed (Spirodela oligorhiza), a nd germinated mung bean (Vigna radiata); the protist is a slime mold (Dicty ostelium discoidium). The tests are based on a crude classification of OPAA s as 'squid type' (DFP hydrolyzed more rapidly than Soman) and all of the o thers termed by us, with questionable justification, as 'Mazur type' (Soman hydrolyzed more rapidly than DFP). Of the two duckweeds, Spirodela oligorh iza hydrolyzes Soman but not DFP, and Lemna minor does not hydrolyze either substrate. In contrast to the report of Yu and Sakurai, mung bean does not hydrolyze DFP and hydrolyzes Soman with a 5-fold stimulation by Mn2+ and a marked inhibition by EDTA. The slime mold hydrolyzes Soman more rapidly th an DFP (but does hydrolyze DFP) and the hydrolysis is Mn2+ stimulated. The failure of these plant sources to hydrolyze DFP is similar to the behavior of OPAA from Bacillus stearothermophilus. Published by Elsevier Science Ire land Ltd.