The basidiomycete QM 806 excreted large amounts of beta-1,3-glucanase into the culture medium. Synthesis and excretion of the enzyme were triggered by a critically low concentration of carbon source. The extracellular beta-1,3-glucanase exhibited a remarkable stability. Addition of glucose or other carbon sources to a culture after consumption of the initial carbon source led to an inactivation of the extracellular beta-1,3-glucanase by an inactivating system, which could be separated from the cells. The inactivation of beta-1,3-glucanse was prevented by cycloheximide. This indicates the necessity of active protein synthesis for the inactivation process but does not prove that the inactivating system itself is a protein. Marked changes in the electrophoretic mobility and immunological properties of beta-1,3-glucanase indicate rather profound alterations of the enzyme protein in the course of inactivation.

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