Effect of tunicamycin on xylanase secretion in the yeast Cryptococcus albidus

The yeast Cryptococcus albidus secretes a glycosylated xylanase (48 kDa) in the culture medium in response to beta-methylxyloside as inducer. Addition of tunicamycin to the medium results in the formation of a modified xylanase (40 kDa) which is depleted in carbohydrate content and whose enzymatic activity is 2.5 times less than that of the glycosylated xylanase. The secretion of xylanase was followed under both conditions by pulse-chase experiments. The half-time of secretion of the glycosylated and nonglycosylated forms was 5 and 2 h, respectively. Cell-associated xylanase activity was not detected when the cells were treated with the antibiotic. The absence of cell wall-associated xylanase, after tunicamycin treatment, was confirmed by immunolocalization with anti-xylanase antibodies at the electron microscopic level. The results suggest that the interactions of carbohydrate moiety within the cell wall retarded the secretion of the enzyme to the medium.