An alkaline protease from fresh fruiting bodies of the edible mushroom Pleurotus citrinopileatus

A protease was purified from fresh fruiting bodies of the edible mushroom Pleurotus citrinopileatus. The isolation procedure included ion exchange chromatography on DEAE- cellulose, CM- cellulose, and Q- Sepharose and fast protein liquid chromatography- gel filtration on Superdex 75. The protease was unadsorbed on DEAE-cellulose and Q- Sepharose, but adsorbed on CM- cellulose. In sodium dodecyl sulfate- polyacrylamide gel electrophoresis, the protease demonstrated a single band with a molecular mass of 28 kDa. The protease showed an optimal pH at 10 and an optimal temperature at 50 C. The activity of the protease was not affected by EDTA, indicating that it is not a metalloprotease. The protease exhibited a higher activity in the presence of K+ and Li+, but its activity was potently inhibited by A1(3+), Cu2+, and Hg2+ ions. It manifested a Km of 3.44 mg/ ml and a V-max of 0.139 mg ml(-1) min(-1). It was devoid of ribonuclease and antifungal activities.