Biosynthesis of -Glucan Microfibrils by Cell-free Extracts from Saccharomyces cerevisiae

Abstract

Glucan synthase activity in cell-free extracts of Saccharomyces cerevisiae was partially stabilized when cells were broken in the presence of sucrose. Under these conditions a significant amount of enzyme activity remained in the supernatant after high-speed centrifugation. When this supernatant fraction was incubated with UDPglucose, microfibrils were synthesized. Microfibrils were insoluble in water, ethanol and acid, and soluble in alkali. Under the electron microscope they appeared more or less uniform with an average length of about 0·5 μm. Alkali-insoluble residue appeared in the form of densely-packed longer microfibrils. After acidification of alkali-solubilized glucan, shorter microfibrils were reprecipitated. Microfibrils were digested by both endo- and exo-1,3-β-glucanase. In the latter case, glucose was the only product indicating that the microfibrils consist of 1,3-β-glucan with no detectable branches.