Role of vacuoles and vesicles in extracellular enzyme secretion from yeast

Preliminary evidence has been obtained which suggests that the intracellular invertase of Saccharomyces cerevisiae may not be localized in the vacuole per se. Alkaline phosphatase, an intracellular enzyme, and acid protease, a typically lysosomal enzyme, both showed high specific activity in the vacuole fraction prepared by equilibrium centrifugation of lysed sphaeroplasts in Ficoll gradients. Invertase activity has been found to be associated with vacuoles only when glucose-repressed cells are derepressed. Cells derepressed for invertase biosynthesis contained a population of vesicles which were virtually absent from the repressed cells. Evidence is presented which strongly suggests that these vesicles rather than the vacuoles are the vehicle by which invertase is secreted from the cell.