PathwayStep972 PathwayStep976 PathwayStep975 PathwayStep974 PathwayStep973 PathwayStep977 Glycogen synthesis Authored: 2003-02-15 00:00:00 GENE ONTOLOGYGO:0005978 Glycogen, a highly branched glucose polymer, is formed and broken down in most human tissues, but is most abundant in liver and muscle, where it serves as a major stored fuel. Glycogen metabolism has been studied in most detail in muscle, although considerable experimental data are available concerning these reactions in liver as well. Glycogen metabolism in other tissues has not been studied as extensively, and is thought to resemble the muscle process (Hers 1976; Lomako et al. 2004; Villar-Palasi and Larner 1970).<p>Glycogen synthesis involves five reactions. The first two, conversion of glucose 6-phosphate to glucose 1-phosphate and synthesis of UDP-glucose from glucose 1-phosphate and UTP, are shared with several other pathways. The next three reactions, the auto-catalyzed synthesis of a glucose oligomer on glycogenin, the linear extension of the glucose oligomer catalyzed by glycogen synthase, and the formation of branches catalyzed by glycogen branching enzyme, are unique to glycogen synthesis. These reactions are shown in the figure. Repetition of the last two reactions generates large, extensively branched glycogen polymers. The catalysis of several of these reactions by distinct isozymes in liver and muscle allows them to be regulated independently in the two tissues. Pubmed15238248 Pubmed183599 Pubmed4320262 Reactome Database ID Release 4370302 Reactome, http://www.reactome.org ReactomeREACT_1736 poly((1,4)-alpha-D-glucosyl) glycogenin => glycogen-glycogenin UTP + D-glucose 1-phosphate <=> pyrophosphate + UDP-glucose 8 UDP-glucose + glycogenin dimer => 8 UDP + {(1,4)-alpha-D-glucosyl}4 glycogenin dimer 8 UDP-glucose + ((1,4)-alpha-D-glucosyl}4 glycogenin => 8 UDP + ((1,4)-alpha-D-glucosyl)8 glycogenin [GYS I form] 8 UDP-glucose + ((1,4)-alpha-D-glucosyl)4 glycogenin => 8 UDP + ((1,4)-alpha-D-glucosyl)8 glycogenin [GYS D form] alpha-D-Glucose 6-phosphate <=> D-Glucose 1-phosphate