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glycogen biosynthesis

General Background : Glycogens "Glycogen" is a megadalton-sized glucose polymer and a major reservoir of readily available energy and carbon compounds in humans. The linkages between the glucose units in glycogen are comprised of approximately 90% alpha-1,4 linkages, with the remainder being alpha-1,6 branch glucosyl linkages. The average chain length is about 12 to 14 glucose units. A key enzyme in the biosynthetic pathway is glycogen synthase. Glycogen synthases utilize : CPD-12575 as the glucosyl group donor. About This Pathway In humans, glycogen is synthesized and stored primarily in liver and muscle cells . Glycogen metabolism is a major component of whole-body glucose metabolism, and defective glycogen storage is associated with several diseases, including type 2 diabetes. The precursor for glycogen synthesis in humans is : CPD-12575, which is produced from :GLC-1-P by the enzyme : CPLX-6973. Initiation of glycogen biosynthesis in mammals is mediated by the enzyme glycogenin (EC 2.4.1.186). This unusual enzyme catalyzes two reactions: first, it transfers one glucose unit from UDP?glucose to form an oligosaccharide covalently attached to itself at a tyrosine residue (Tyr194). Next it catalyzes the addition of additional glucose units to the first one by alpha-1,4-glucosidic linkages, forming a glycogen primer . The human :CPLX-6975, which is a homotetramer of 85 kDa subunits, attaches to the glucosylated glycogenin complex, and catalyzes the transfer of the glucose moiety of additional : CPD-12575 molecules by alpha-1,4-glucosidic linkage, extending the glycogen chain further. During this elongation process, branched alpha-1,6-glucosidic linkages are formed by the : HS03772-MONOMER, which cuts groups of ~6 glucose units from the end of the chains, and reattaches them by alpha-1,6-linkages, forming branched points. This process continues, forming a complex termed proglycogen, which is about 400 kDa. At this point, a different glycogen synthase, with a lower affinity for : CPD-12575, replaces the previous synthase, and along with the branching enzyme, catalyzes the synthesis of a final macroglycogen polymer, which is about 10,000 kDa .

from BIOCYC source record: HUMAN_PWY-5067
Type: pathway
Taxonomic scope
:
organism-specific biosystem
Organism
:
Homo sapiens
BSID:
142202

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