S. Derek Killilea
Metabolic Regulation via Protein Kinases and Phosphatases
Glycogen is the storage form of glucose in mammalian cells. In liver it serves as a source of blood glucose in the fasted state while in muscle it serves as a source of glucose for energy production by glycolysis under anaerobic conditions. The metabolism of this highly-branched glucan is regulated by hormonal and neural signals that control the actions of protein kinases and phosphatases acting on the enzymes that form (glycogen synthase) and break, via phosphorylesis, (glycogen phosphorylase) the alpha-1,4 glycosidic linkages of the polysaccharide chains. In vivo these enzymes and their regulating kinases and phosphatases are associated with the glycogen chains via glycogen storage sites that are separate from the catalytic sites. These interactions are not passive events as shown in the case of phosphorylase where this binding results in the conversion of the enzyme to its active dimeric form. In addition, it has been shown that the phosphorylation and activation of phosphorylase by phosphorylase kinase is stimulated by glycogen. Our current interests are in determining the affinity of these enzymes for glycogen preparations having defined outer chain lengths. In addition, we are interested in identifying the glycogen storage sites of these enzymes and in determining if glycogen stimulation of the phosphorylase kinase catalyzed reaction is due to interaction(s) of the polysaccharide with the kinase, its substrate phoshphorlyase, or with both.
Killilea, S.D., Cheng, Q., and Wang, Z.-X. (1998). Protein Phosphatase Type 1 and Type Assays. In: “Methods in Molecular Biology” (J. W. Ludlow, ed.), 93, p.23-33, Humana Press, Totowa, New Jersey.