Exo-(1→3)-β-glucanase, β-glucosidase, autolysin and trehalase were assayed in during yeast growth, starvation and germ-tube formation. Cell viability, germ-tube formation, intracellular glucose-6-phosphate dehydrogenase and β-glucosidase were unaffected in cells incubated in 0.1 M-HC1 for 15 min at 4 °C. However, trehalase, (1 → 3)-β-glucanase and autolysin activities in acid-treated cells decreased by 95, 50 and 35% respectively, indicating that these enzymes are, in part, associated with the cell envelope. Trehalase activity increased throughout yeast growth and remained elevated during the first hour of incubation for germ-tube formation. All of the trehalase activity in starved yeast cells could be measured without the permeabilizing treatment. β-Glucosidase activity declined throughout yeast growth and did not alter during germ-tube formation. Both the (l→3)-β-glucanase and autolysin activities were optimal at pH 5.6, inhibited by gluconolactone and HgCl, and maximal at 15-16 h during yeast growth. Although autolysin activity increased by 50-100% when starved yeast cells were incubated for germ-tube formation, the (1 →3)-β-glucanase remained constant. When acid-treated starved yeast cells were similarly induced, (1→3)-β-glucanase increased 100% over 3 h of germ-tube formation. Yeast cells secreted (1→3)-β-glucanase into the growth medium. This was highest in early exponential phase cultures (34% of the maximum activity) and declined throughout growth. (1 →3)-β-Glucanase was also secreted into the medium during germ-tube formation and this represented 80-100% of the activity in germ-tube forming cells. Both secretion of (1→3)-→-glucanase and germ-tube formation were inhibited by 2-deoxyglucose, ethidium bromide, trichodermin and azaserine.


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