Glycogen is a glucose polymer stored in prokaryotic and eukaryotic cells. This macromolecule acts as an energy reserve providing protection against temporary starvation conditions in microorganisms and functioning in tissue-specific roles in animals and humans. Glycogen is synthesized by the coordinated actions of glycogen synthase and the branching enzyme, while its degradation is catalyzed by two independent pathways. In the cytosolic pathway, glycogen phosphorylase, in conjunction with the debranching enzyme, degrades glycogen. In the lysosomal pathway, termed glycophagy, glycogen is degraded by alpha-glucosidase. Both glycogen synthase and glycogen phosphorylase are highly regulated by processes including covalent phosphorylation, small molecule effectors, and cellular location. Glycogen metabolism has been studied in a wide variety of model systems including bacteria, yeast, roundworms, fruit flies, fish, birds, rodents, livestock, and humans. These studies have examined the role of glycogen in physiological conditions as well as in the context of naturally occurring and genetically engineered mutations in glycogen metabolizing enzymes. Methods for monitoring glycogen metabolism include measurement of the glucose polymer in microorganisms, cell culture, individual muscle fibers, and assorted tissues with biochemical, histochemical, and immunohistochemical techniques. The use of non-invasive techniques such as ultrasound and ¹³C NMR spectroscopy facilitates the measurement of glycogen in conscious human muscle and the human brain, respectively. Key enzymes in glycogen synthesis and degradation are also measured regarding enzymatic activity, expression level, phosphorylation state, and cellular location.

This Method Collection aims to bring together both routine and novel techniques for monitoring glycogen metabolism in varied model systems.