Evidence for glycogen structures associated with plasma membrane invaginations as visualized by freeze-substitution and the Thiery reaction in Saccharomyces cerevisiae

We have used a combination of freeze-substitution electron microscopy and s pecific reaction for polysaccharides to re-evaluate glycogen structures in Saccharomyces cerevisiae. We also used mutant cells devoid of glycogen to c onfirm the glycogenic nature of the structures described. Previously descri bed cytoplasmic aggregates were confirmed as glycogen granules. Moreover, a n original structure was discovered. This is a ring of glycogen surrounding a finger- or pleat-like plasma membrane invagination. This structure could be physiologically significant in terms of channelling glucose to or from glycogen reserves.