Glycogen storage diseases

Abstract

Glycogen is the storage form of glucose in virtually all animal cells, but it is most abundant in liver and muscle (7,15,31). Glycogen is a highly branched polymer with a treelike structure that can accommodate up to 60,000 glucose units in a single globular molecule with a molecular mass of approximately 10,000 kDa (2,7,31). Because of this unique structure, 7% to 10% of the glucose residues are terminal and thus easily accessible to the action of both biosynthetic and degradative enzymes. When viewed by transmission electron microscopy (TEM), glycogen molecules are easily recognized as spherical electron-dense particles approximately 30 nm in diameter. These spherules are called b particles. In the liver, where the concentration of glycogen is considerably higher than in other tissues, b particles form large rosetteshaped aggregates ranging in size from 110 to 150 nm and reaching molecular weights as high as 100,000 kDa (7,31). These structures are called a particles.