CHARACTERIZATION OF EPOXIDE HYDROLASE ACTIVITY IN ALTERNARIA-ALTERNATA F SP. LYCOPERSICI - POSSIBLE INVOLVEMENT IN TOXIN PRODUCTION - EPOXIDE HYDROLASE IN ALTERNARIA-ALTERNATA F SP. LYCOPERSICI

Using trans-diphenylpropane oxide (tDPPO) as a substrate, we measured epoxide hydrolase (EH) activity in subcellular fractions of Alternaria alternata f. sp. lycopersici (Aal), a fungus that produces host-speci fic toxins. The activity was mainly (>99.5%) located in the soluble fr action (100,000 x g supernatant) with the optimum pH nf 7.4. An increa se of toxin production between days 3 and 9 found in a Aal liquid cult ure over a 15 days period was concomitant with a period of high EH act ivity. EH activity remained constant during the same period in an Alte rnaria alternata culture, a fungus which does not produce toxin. In vi vo treatment of Aal culture with the peroxisome proliferator clofibrat e stimulated EH activity by 83% and enhanced toxin production 6.3 fold . Both 4-fluorochalcone oxide (4-FCO) and (2S,3S)-(-)-3-(4-nitrophenyl )-glycidol (SS-NPG) inhibited EH activity in vitro with a I-50 of 23 /- 1 mu M and 72 +/- 19 mu M, respectively. The possible physiological substrate 9,10-epoxystearic acid was hydrolyzed more efficiently by A al sEH than the model substrates trans-and cis-stilbene oxide (TSO and CSO) and trans-and cis-diphenylpropane oxide (tDPPO and cDPPO).