ABSTRACT
Organisms have complex and sophisticated systems for harvesting, storing, and mobilizing energy in the form of carbohydrates. Energy is primarily stored in carbohydrates in the form of the polysaccharides glycogen and starch. While polysaccharide synthesis and degradation has been studied for many decades, regulation of carbohydrate storage via reversible phosphorylation by dikinase and phosphatase enzymes has only recently been identified. The discovery of these enzymes is intimately linked to the discovery of aberrantly formed glycogen and starch in humans and plants, respectively. These aberrant forms of the polysaccharides contain atypical levels of phosphate and abnormal architecture, and have revealed key roles for reversible phosphorylation in glycogen and starch synthesis and metabolism. This chapter reviews the discovery and enzymology of the glucan phosphatase and dikinase enzymes involved in phosphorylation-mediated regulation of storage carbohydrates and how they function in carbohydrate metabolism. These findings are placed in the context of outstanding questions regarding the biology and utilization of reversible carbohydrate phosphorylation.
