**2.1 Glycogen synthesis**

Two enzymes, glycogen synthase and glycogen phosphorylase, control glycogen levels. Both enzymes are regulated by phosphorylation and allosteric modulators. Specifically in the fed state, insulin activates glycogen synthase (limiting enzyme for glycogen synthesis) by promoting its dephosphorylation and, at the same time inhibits glycogen phosphorylase (important for glycogen breakdown). Meanwhile, glucose-6-phosphate binding to glycogen synthase favours its dephosphorylation, promoting glycogen synthase activity (Bollen, 1998; Agius, 2008). As a result, glucose coming from bloodstream fills hepatic glycogen stores.
