α- d-mannosidase of Saccharomyces cerevisiae Characterization and modulation of activity

Abstract

A unique and interesting α- d-mannosidase (α- d-mannoside mannohydrolase, EC 3.2.1.24) activity has been isolated from Saccharomyces cerevisiae. The enzyme was localized in a crude particulate fraction of the cell extract and was not solubilized by treatment with detergents or high ionic strength NaCl. The enzyme had a pH optimum of 6.3, K m 50 μM with p- nitrophenyl-α- d-mannopyranoside , and was competitively inhibited by d-mannose ( K i 20 mM). The enzyme is not affected by ethylenediaminetetraacetic acid, a number of different cations, or sulfhydryl reagents. It was inhibited by p-chloromercuriphenyl sulfonic acid and this inhibition is prevented by the addition of substrate. The cellular concentration of α- d-mannosidase is inversely proportional to growth rate, suggesting that the enzyme is under catabolite repression. The level of enzyme was found to increase approx. 8-fold during sporulation. This is apparently due to de novo synthesis, since inhibition of protein synthesis by cycloheximide prevents the increase in enzyme activity.