Discovery of multiple organofluorophosphate hydrolyzing activities in the protozoan Tetrahymena thermophila

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Abstract
Recently it has been found that homogenates of Tetrahymena thermophila can hydrolyze the potent acetylcholinesterase inhibitors O,O‐diisopropylphosphofluoridate (DFP) and O‐1,2,2‐trimethylpropylmethylphosphonofluoridate (soman). Upon purification of the DFP hydrolyzing activity 10‐fold it had been noted that the soman hydrolyzing activity increased only 2–3 fold. Treatment with manganous ion and comparison of the soman and DFP hydrolysis rates of the homogenate indicated that a mixture of the squid‐type and Mazur‐type DFPases may be present. Subsequent purification of the enzymatic activities within the Tetrahymena‐homogenate demostrated that there are at least five functioning proteins of molecular weights 67 000 to 96 000. None are directly homologous to the DFPases found in hog kidney or squid. The enzymatic activities are designated DFPase‐1 through DFPase‐5. A hypothesis is presented that the functions of DFPases are in the normal metabolism of organophosphates naturally synthesized by T. thermophila.