Phosphorylase phosphatase and flash activation of skeletal muscle glycogen phosphorylase-A tribute to Edmond H. Fischer

Glycogen is a polymerized form of glucose that serves as an energy reserve in all types of organisms. In animals glycogen synthesis and degradation, especially in liver and skeletal muscle, are regulated by hormonal and physiological signals that reciprocally control the opposing activities of glycogen synthase and glycogen phosphorylase. These enzymes are under allosteric control by binding of metabolites (e.g., ATP, AMP, G6P) and covalent control by reversible phosphorylation by kinase and phosphatase all assembled together on glycogen. More than 50 years ago Edmond Fischer and colleagues showed flash activation of phosphorylase in glycogen particles. This involved transient and extensive inhibition of protein phosphatase but even today the phenomenon is not understood. Phosphatase regulation is known to rely on regulatory subunits including glycogen binding subunits that serve as scaffolds, binding catalytic subunit, glycogen, and substrates. This tribute article to Edmond Fischer highlights his thoughts and ideas about the transient inhibition of phosphorylase phosphatase during flash activation of phosphorylase and speculates that phosphatase regulation in glycogen particles might involve a/b hybrids of phosphorylase.

Automated summary

Glycogen is a polymerized form of glucose used as an energy reserve in organisms. The synthesis and degradation of glycogen in animals, especially in the liver and skeletal muscle, is regulated by hormones and physiological signals that control the activities of glycogen synthase and glycogen phosphorylase. This article discusses the flash activation of phosphorylase in glycogen particles and suggests that the regulation of phosphatase in glycogen particles may involve hybrids of phosphorylase.