An examination of factors affecting the instability of Saccharomyces cerevisiae glucan synthetase in cell free extracts.

Yeast beta(1--3) glucan synthetase is stimulated and stabilized by EDTA. Sucrose protects the enzyme from self-inactivation. Preincubation of cell free extracts at low sucrose concentrations indicates a slow transition of the enzyme towards dissociation. Transition kinetics at 30 degrees C and 0 degrees C in the presence and in the absence of sucrose are interpreted assuming that a subunit is thermolabile in the free state and that sucrose increases its stability. Magnesium is deleterous for glucan synthetase in cell-free extracts. Chaotropic agents inactivate glucan synthetase according to their capacity to solubilize and depolymerize biological compounds. Fluoride plays a special role in the activation of glucan synthetase. Its action appears to be dependent on the presence of GTP (or other nucleotides). The role of all these agents on the activity and stability of the enzyme is interpreted in a unified scheme.