ABSTRACT
Covalent modifications are chemical groups that are added to pre-existing macromolecular structures. The α-glucans glycogen and starch both contain phosphate esters. In plants, several enzymes are known to phosphorylate and dephosphorylate starch. Processes of glycogen phosphorylation are largely unclear. Laforin has been described as the only glycogen phosphatase. In starch, phosphate is implicated in physicochemical changes at the granule surface that are important for efficient starch turn-over. While glycogen phosphate has gained importance in the context of Lafora disease where glycogen is hyperphosphorylated due to deficiencies in the proteins laforin or malin, the exact role of phosphate in glycogen metabolism is still under investigation. Appropriate methods for the analyses of glucan phosphate are essential. After a brief summary of the current knowledge of α-glucan phosphorylation, this chapter gives a wide overview of methodological approaches that aim to characterize glucan phosphate qualitatively and quantitatively. This includes discussion of chemical and enzymatic phosphate assays as well as of approaches that combine chromatography mass spectrometry. Methods used to investigate the enzymology underlying glucan phosphorylation and dephosphorylation, and finally the principle and general findings of NMR studies on glucan phosphate are described.
