Derepression of beta-1,3-glucanases in Penicillium italicum: localization of the various enzymes and correlation with cell wall glucan mobilization and autolysis

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Abstract
The localization of the derepressible .beta.-1,3-glucanases of P. italicum and the cell wall autolysis under conditions of .beta.-1,3-glucanase derepression (24 h in a low-glucose medium) were studied. About 15% of the total activity was secreted into the culture medium during the 24 h period and consisted of similar amounts of each of the 3 .beta.-1,3-glucanases (I, II, III) produced by this species. Treatment of derepressed mycelia with periplasmic enzyme-inactivating agents resulted in a loss of 45% of the mycelium-bound .beta.-1,3-glucanase. Analysis of periplasmic enzymes solubilized by 2 M NaCl or by autolysis of isolated cell walls revealed that only .beta.-1,3-glucanases II and III were bound to the cell wall. These 2 enzymes were capable of releasing in vitro reducing sugars from cell walls, whereas .beta.-1,3-glucanase I was not. The autolytic activity of cell walls isolated from derepressed mycelium was greater than that of cell walls isolated from repressed mycelium. The incubation of the fungus in the low-glucose medium also resulted in the in vivo mobilization of 34% of the cell wall .beta.-1,3-glucan, and this mobilization was fully prevented by cycloheximide, which also blocked derepression of .beta.-1,3-glucanases. Derepression of .beta.-1,3-glucanase seems to be coupled to the mobilization of cell wall glucan.