A survey of proteases in edible mushrooms with synthetic peptides as substrates

The protease activities in six edible mushrooms were surveyed using synthetic fluorogenic substrates that have different specificities for each protease group. The activity was determined by measuring the fluorogenic intensity of the 7-amino-4-methylcoumarin (AMC) liberated by an enzyme. Various types of activities were found in all mushrooms, and their activities depended largely on the mushroom species, but also on the pH and localization. Flammulina velutipes and Pleurotus eryngii had the widest and highest proteolytic activities among the six mushrooms examined. The proteasome-like protease activities were generally much higher than those of other proteases. High caspase activities, which occur during apoptosis in cells, were detected in two mushrooms, F. velutipes and Hypsizigus marmoreus. The pH optima of the proteolytic activities were largely divided into two groups, acidic pH 5-6 for caspases and neutral to alkaline (pH 6.5-11) for the others. In F. velutipes, higher proteolytic activity was observed in the basement of the stem than in the cap and stem. Purification and characterization of protease were also carried out to identify a protease from Grifola frondosa using t-butyloxycarbonyl-Leu-Arg-Arg-4-methylcoumaryl-7-amide (Boc-LRR-MCA) as the substrate.