Thallus samples of Evernia prunastri (L.) Ach., floated on 40 mM L-arginine in the light, develop maximal arginase (EC 22.214.171.124.) activities at 4h and 12h incubation, corresponding to two forms of the enzyme with molecular weights of 330 kDa and 264 kDa, respectively. A different arginase, synthesized by talli incubated for 8h on 40 μΜ cycloheximide, has an aopparent molecular weight of 380 kDa. These three arginases have been purified and showed Km values for L-arginine of 2.1 mM (for the enzyme which is mainly produced at 4h culture), 1.92 mM (at 12h culture) and 1.44 mM (for the remaining activity after 8h culture on cycloheximide), as deduced from the double-reciprocal plots. These kinetic data are compared with those of other arginases from the same lichen species.
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