Schematic representation of glycogen synthesis and breakdown in the cytosol. The precursor used for glycogen synthesis comprises UTP-activated glucose units (UDPglucose).
Glycogen synthesis in the cytosol begins with the formation of glycogenin (GYG)-bound oligosaccharide primers and proceeds with the elongation of the primers by
glycogen synthase (GYS), which binds activated glucose units to the non-reducing end of the forming glycogen chain. Glycogen degradation consists on the phosphorolytic
cleavage of glucose-1-P, catalysed by glycogen phosphorylase (PYGL/B/M), and the removal of branches catalysed by the debranching enzyme (DBE). DBE transfers three
glucose blocks to another glycogen chain, and then hydrolytically cleaves the remaining glucose of the branch, generating free glucose. Glycogen-derived glucose-1-P and free
glucose can enter the glycolytic or the pentose phosphate pathway (PPP). HK: hexokinase; glucose-6/1-p: glucose-6/1-phosphate; PGM: phosphoglucomutase; UGP: UDPglucose
pyrophosphatase; UDP-glucose: uridine diphospho-glucose; GYG: glycogenin; GYS: glycogen synthase; GBE: glycogen branching enzyme; PYGL/B/M: glycogen
phosphorylase, liver/brain/muscle; DBE: debranching enzyme; PPP: pentose phosphate pathway.
Schematic representation of glycogen synthesis and breakdown in the cytosol. The precursor used for glycogen synthesis comprises UTP-activated glucose units (UDPglucose).Glycogen synthesis in the cytosol begins with the formation of glycogenin (GYG)-bound oligosaccharide primers and proceeds with the elongation of the primers byglycogen synthase (GYS), which binds activated glucose units to the non-reducing end of the forming glycogen chain. Glycogen degradation consists on the phosphorolyticcleavage of glucose-1-P, catalysed by glycogen phosphorylase (PYGL/B/M), and the removal of branches catalysed by the debranching enzyme (DBE). DBE transfers threeglucose blocks to another glycogen chain, and then hydrolytically cleaves the remaining glucose of the branch, generating free glucose. Glycogen-derived glucose-1-P and freeglucose can enter the glycolytic or the pentose phosphate pathway (PPP). HK: hexokinase; glucose-6/1-p: glucose-6/1-phosphate; PGM: phosphoglucomutase; UGP: UDPglucosepyrophosphatase; UDP-glucose: uridine diphospho-glucose; GYG: glycogenin; GYS: glycogen synthase; GBE: glycogen branching enzyme; PYGL/B/M: glycogenphosphorylase, liver/brain/muscle; DBE: debranching enzyme; PPP: pentose phosphate pathway.
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