Editing Glycogenolysis (section)

==Mechanism==

In the muscles, glycogenolysis begins due to the binding of [[Cyclic adenosine monophosphate|cAMP]] to [[phosphorylate kinase]], converting the latter to its active form so it can convert phosphorylase b to [[phosphorylase a]], which is responsible for catalyzing the breakdown of glycogen.<ref>{{cite book |last1=Paredes-Flores |first1=M. A. |last2=Rahimi |first2=N. |last3=Mohiuddin |first3=S. S. |title=Biochemistry, Glycogenolysis |date=9 January 2024 |publisher=StatPearls Publishing |pmid=32119304 |url=https://pubmed.ncbi.nlm.nih.gov/32119304/}}</ref>

The overall reaction for the breakdown of glycogen to glucose-1-phosphate is:<ref name=":0" />
: glycogen<sub>(n residues)</sub> + P<sub>i</sub> {{eqm}} glycogen<sub>(n-1 residues)</sub> + glucose-1-phosphate
Here, [[glycogen phosphorylase]] cleaves the bond linking a terminal glucose [[Residue (chemistry)|residue]] to a glycogen branch by [[Substitution reaction|substitution]] of a [[phosphoryl]] group for the α[1→4] linkage.<ref name=":0" />

Glucose-1-phosphate is converted to [[glucose-6-phosphate]] (which often ends up in [[glycolysis]]) by the enzyme [[phosphoglucomutase]].<ref name=":0" />

Glucose residues are phosphorolysed from branches of glycogen until four residues before a glucose that is branched with a α[1→6] linkage. [[Glycogen debranching enzyme]] then transfers three of the remaining four glucose units to the end of another glycogen branch. This exposes the α[1→6] branching point, which is [[hydrolysis|hydrolysed]] by [[glucosidase|α[1→6] glucosidase]], removing the final glucose residue of the branch as a molecule of glucose and eliminating the branch. This is the only case in which a glycogen metabolite is not glucose-1-phosphate. The glucose is subsequently phosphorylated to glucose-6-phosphate by [[hexokinase]].<ref name=":0" />