Thallus samples of Evernia prunastri floated on 40 mM L-arginine for 4h in the light produce an induced arginase activated by ervernic acid, with an apparent Km value of 0.23 mM. After 12h incubation in the same conditions, induced arginase is activated by atranorin, with an apparent Km value of 0.16 μΜ. Evernic acid and atranorin, at 4h and 12h incubation, respectively, are the only water-soluble phenols retained in the cell-free extracts, whereas D-usnic acid behaves as a medullar, water-insoluble lichen phenol. A different, constitutive arginase, activated after 8h incubation of lichen thalli on 40 μΜ cycloheximide in the light, is also activated b y atranorin, the only water-soluble phenol in cell-free extracts obtained at this time, with an apparent Km value of 33μΜ. A model of regulation of these arginases by evernic acid and atranorin is proposed.
085 - 096