Purification of protease Dried fruiting bodies of C. sobolifera mushrooms (25 g) were homogenized and extracted overnight in 0.15 M NaCl at 4°C. The homogenate was centrifuged at 8000×g for 20 min, and then (NH4)2SO4 was added to the supernatant to 70% saturation. Four hours later, the precipitate was collected by centrifugation at 6000×g for 30 min. The precipitate was dissolved and dialyzed to remove (NH4)2SO4 before loading onto an anion-exchange column (2.5×20 cm) of DEAE-cellulose pre-equilibrated with 10 mM NH4HCO3 buffer (pH 9.4). The column was eluted with the same buffer. After removal of the unadsorbed peak (fraction D1) containing strong protease activity, two adsorbed peaks, fractions D2 and D3 were eluted with 100 mM and 1 M NaCl, respectively, in the starting buffer. The active fraction (D1) was next subjected to a cation-exchange column (1.0×15 cm) of SP- Sepharose pre-equilibrated in 10 mM citric acid buffer (pH 5.0). After removal of unadsorbed proteins (fraction SP1), the column was eluted with a linear concentration gradient of 0–800 mM NaCl in 10 mM citric acid buffer (pH 5.0) to obtain adsorbed proteins (fractions SP2 and SP3). The active fraction (SP3) with protease activity was subsequently purified on a Superdex 75 HR 10/30 column in 0.15 M NH4HCO3 buffer (pH 8.5) by fast protein liquid chromatography (FPLC) using an AKTA Purifier (GE Healthcare). The first fraction (SU1) contained the purified protease.