Intracellular activity of mycelial proteinases during fruit-body development in Flammulina velutipes

Abstract

In the mycelium of Flammulina velutipes cultured on potato–glucose solution the concentration of water-soluble protein began to decrease steeply before fruit bodies formed, but the total amount of protein per culture decreased only when fruit bodies began to elongate rapidly. The level remained very low during rapid elongation. Proteinase activity per unit weight of mycelium against milk protein and azoalbumin decreased in parallel with the concentration of mycelial protein. Activity against azure blue – hide powder was low until the onset of rapid fruit-body elongation and reached a maximum later during that phase. Azoalbumin was hydrolyzed more actively than hide powder. Proteolytic activity per gram of mycelium against mycelial protein was almost the same before fruiting as during rapid fruit-body elongation. Specific activities per milligram protein against the three types of nonnative substrates increased in parallel to a maximum late during rapid elongation when protein concentration was lowest. Specific activity against native mycelial protein was also higher in extracts from older mycelia. Proteolysis was optimal near neutral pH and very low at pH 3.2. Tests with group-specific proteinase inhibitors showed that metallo-proteinases predominate in the mycelium. Serine, and to a lesser extent carboxyl and thiol proteinases, were also present. Neither endogenous inhibitors nor activators of proteolysis were detected.