Multiple epoxide hydrolases in Alternaria alternata f. sp lycopersici and their relationship to medium composition and host-specific toxin production

The production of Alternaria alternata f. sp. lycopersici host-specific tox ins (AAL toxins) and epoxide hydrolase (EH) activity were studied during th e growth of this plant-pathogenic fungus, in stationary liquid cultures. Me dia containing pectin as the primary carbon source displayed peaks of EH ac tivity at day 4 and at day 12. When pectin was replaced by glucose, there w as a single peak of EH activity at day 6. Partial characterization of the E H activities suggests the presence of three biochemically distinguishable E H activities. Two of them have a molecular mass of 25 kDa and a pI of 4.9, while the other has a molecular mass of 20 kDa and a pi of 4.7. Each of the EH activities can be distinguished by substrate preference and sensitivity to inhibitors. The EH activities present at day 6 (glucose) or day 12 (pec tin) are concomitant with AAL toxin production.