Abstract
Summary Evernia prunastri synthesizes urease induced by urea exogenously supplied or endogenously produced from accumulated arginine. In the latter case, the maximum of enzyme activity is 26 times lower than that found when lichen thalli are floated on 40 mM urea. Tolbutamide, a urea derivative with a K i value of 3.6 μM, competitively inhibits urease. As a consequence, urease activity is not detected when 10 μM tolbutamide is supplied to lichen thalli. CO 2 evolved after urea hydrolysis is, in part, used to produce lichen phenolics. Thus, accumulation of atranorin, chloroatranorin and evernic acid is enhanced by a supply of 40 mM urea. However, usnic acid is slightly produced when the lichen thallus mobilizes its own urea. Tolbutamide impedes accumulation of these four phenolics.
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