Effect of Tunicamycin on Exo-1,3- -D-glucanase Synthesis and Secretion by Cells and Protoplasts of Saccharomyces cerevisiae

Addition of tunicamycin to the culture medium of growing Saccharomyces cerevisiae protoplasts or cells resulted in the formation of a modified exo-1,3-beta-D-glucanase which was detectable in both extracellular and intracellular fractions. This modified enzyme had a lower molecular weight than the native form and did not bind to concanavalin A. The activation energy and Km values of both enzyme forms were identical. Antibodies raised against the native protein readily precipitated the exo-1,3-beta-D-glucanase produced after tunicamycin treatment. The latter enzyme was comparable, in terms of molecular size and lack of affinity for concanavalin A, to the beta-D-glucanase obtained by treatment of the native form with endoglycosidase H; both lacked the carbohydrate moiety present in the native enzyme. The exo-1,3-beta-D-glucanase obtained in the presence of the antibiotic was more sensitive to variations in temperature and pH than both endoglycosidase H-treated and non-treated enzymes. Our results suggest that the carbohydrate moiety, if not necessary for exo-1,3-beta-D-glucanase secretion, may play a role in the conformation of the protein and in stabilizing the enzymic activity.