Conversions of deoxyradicinin to radicinin and of radicinin to 3-epi-radicinin in the phytopathogenic fungus Bipolaris coicis.

Radicinin is a phytotoxic and antibiotic metabolite produced by some phytopathogenic fungi. Precursor administration and cell-free experiments with deoxyradicinin and radicinin were carried out in Bipolaris coicis H13-3. When deoxyradicinin was administered to the fungus, radicinin and 3-epi-radicinin formed. When radicinin administered, 3-epi-radicinin was formed. Their formation was confirmed by cell-free experiments. Deoxyradicinin 3-monooxygenase which catalyzes conversion of deoxyradicinin to radicinin showed the best activity at 35 °C and pH 7.0, and required NAD+ as co-enzyme. Its molecular weight was determined to be 130-184 kDa. Radicinin epimerase catalyzing the reaction of radicinin to 3-epi-radicinin was purified from a cell-free extract. Radicinin epimerase is a homodimer of a 28 kDa subunit, and its highest activity was achieved at 30-35 °C and pH 7.0-9.0.