8 UDP-glucose + ((1,4)-alpha-D-glucosyl)4 glycogenin => 8 UDP + ((1,4)-alpha-D-glucosyl)8 glycogenin [GYS D form] EC Number: 2.4.1.11 Phosphorylated glycogen synthase catalyzes the addition of glucose residues to the non reducing end of a (1,4)-alpha-D-glucose multimer formed on glycogenin 1 or 2 when activated by glucose 6-phosphate. (Here the addition of four glucose residues is annotated.) The enzyme is associated with glycogen granules in the cytosol.<p>Glycogen synthase proteins are encoded by two human genes, GYS1 and GYS2. GYS1 protein is abundant in skeletal muscle while GYS2 is abundant in liver. The cytosolic location and glycogen synthase activity of GYS1 protein has been demonstrated in studies of wild-type and mutant proteins expressed in cultured cells in vitro (Cid et al. 2000). Defects in GYS1 protein in vivo are associated with deficient muscle glycogen synthesis and exercise intolerance in vivo (Kollberg et al. 2007). The enzymatic activity of purified GYS2 protein has been characterized experimentally (Westphal and Nuttall 1992). Defects in GYS2 protein in vivo are associated with fasting hypoglycemia and defective glycogen synthesis in the liver (Orho et al. 1998).<p>GYS activity is regulated by phosphorylation. In its phosphorylated “D” form, annotated here, enzyme activity requires the presence of glucose 6-phosphate. The structure and activity of phosphorylated human GYS protein tetramers are inferred from the properties of the rabbit GYS1 (skeletal muscle) protein which has been purified and characterized in detail (Soderling et al. 1970). Pubmed10924520 Pubmed1731614 Pubmed17928598 Pubmed4320836 Pubmed9691087 Reactome Database ID Release 4371574 Reactome, http://www.reactome.org ReactomeREACT_1053 has a Stoichiometric coefficient of 8 oligo((1,4)-alpha-glucosyl) glycogenin dimer poly((1,4)-alpha-glucosyl) glycogenin dimer