ABSTRACT
Biosynthesis of the energy storage molecule glycogen is vital, allowing the localised accumulation of glucose chains in soluble, highly branched particles. The specific role of glycogen depends on the tissue of synthesis, with the highest concentrations found in the liver, which acts to buffer blood glucose concentrations. Skeletal muscle relies on glycogen to fuel fibre contractions essential to our locomotion. Glycogen is also found in the heart, brain, skin, kidney, adipose tissue and in the placenta. The importance of a functioning glycogen metabolism is highlighted by the wide array of pathologies that result from its alteration or disruption. This ranges from exercise intolerance and cardiac arrest when glycogen levels are reduced to the accumulation of deadly neurotoxic “polyglucosan bodies” when glycogen’s chain-length diverges from normal physiological conditions. This chapter summarises the molecular structure of glycogen, its numerous physiological roles, the metabolic pathways feeding into glycogen synthesis and the main enzymes involved in glycogen’s synthesis and degradation. The remaining sections of the chapter review the numerous glycogen storage diseases (GSDs) and discuss the mechanisms that lead to polyglucosan formation, a common feature in many of the GSDs discussed.
