PathwayStep991 PathwayStep992 PathwayStep990 PathwayStep988 PathwayStep989 PathwayStep984 PathwayStep985 PathwayStep986 PathwayStep987 PathwayStep980 PathwayStep981 PathwayStep982 PathwayStep983 PathwayStep979 Glycogen breakdown (glycogenolysis) Authored: 2003-02-15 00:00:00 GENE ONTOLOGYGO:0005980 Glycogen breakdown occurs via the same chemical steps in all tissues but is separately regulated via tissue specific isozymes and signaling pathways that enable distinct physiological fates for liver glycogen and that in other tissues. Glycogen phosphorylase, which can be activated by phosphorylase kinase, catalyzes the removal of glucose residues as glucose 1-phosphate from the ends of glycogen branches. The final four residues of each branch are removed in two steps catalyzed by debranching enzyme, and further glycogen phosphorylase activity completes the process of glycogen breakdown. The figure shows the actions of phosphorylase and debranching enzyme. The first glucose residue in each branch is released as free glucose; all other residues are released as glucose 1-phosphate. The latter molecule can be converted to glucose 6-phosphate in a step shared with other pathways (Villar-Palasi and Larner 1970; Hers 1976). Pubmed183599 Pubmed4320262 Reactome Database ID Release 4370221 Reactome, http://www.reactome.org ReactomeREACT_1008 D-Glucose 1-phosphate <=> alpha-D-Glucose 6-phosphate poly((1,4)-alpha-glucosyl) glycogenin-2 + n orthophosphate => glycogenin-2 + n D-glucose 1-phosphate [PYGL] ((1,6)-alpha-glucosyl)poly((1,4)-alpha-glucosyl)glycogenin => poly{(1,4)-alpha-glucosyl} glycogenin + alpha-D-glucose poly((1,4)-alpha-glycosyl) glycogenin-1 + n orthophosphate => glycogenin-1 + n D-glucose 1-phosphate [PYGM,PYGB] glycogen-glycogenin-2 + n orthophosphate => limit dextrin-glycogenin-2 + n D-glucose 1-phosphate [PYGL] limit dextrin-glycogenin => ((1,6)-alpha-glucosyl)poly((1,4)-alpha-glucosyl) glycogenin PGYM b dimer:AMP complex <=> PGYM dimer, b form + 2 AMP glycogen-glycogenin-1 + n orthophosphate => limit dextrin-glycogenin-1 + n D-glucose 1-phosphate [PYGM,PYGB] PGYB dimer, b form + 2 AMP <=> PGYB b dimer:AMP complex glycogen phosphorylase (PYGL) dimer b + 2 ATP => glycogen phosphorylase (PYGL) dimer a + 2 ADP PGYM dimer, b form + 2 AMP <=> PGYM b dimer:AMP complex PGYB b dimer:AMP complex <=> PGYB dimer, b form + 2 AMP glycogen phosphorylase (PYGB) dimer b + 2 ATP => glycogen phosphorylase (PYGB) dimer a + 2 ADP glycogen phosphorylase (PYGM) dimer b + 2 ATP => glycogen phosphorylase (PYGM) dimer a + 2 ADP