glykogeenogeneesiä

Glykogeenogeneesiä, or glycogenogenesis, is the biological process by which glycogen is synthesized from glucose in the body. This pathway is crucial for maintaining blood glucose levels during fasting or increased energy demand. In liver cells, glucose is first activated to glucose-6-phosphate by hexokinase or glucokinase. The glucose-6-phosphate then undergoes isomerization to glucose-1-phosphate by phosphoglucomutase. This activated form serves as the substrate for glycogen synthase, the key enzyme that links glucose units to a growing glycogen chain.

The glycogen synthase reaction adds UDP-glucose to the non-reducing ends of existing glycogen chains, forming α(1→4) glycosidic bonds. Branching enzyme, or glycogen branching enzyme (GBE1), introduces α(1→6) branch points approximately every 24–30 residues, enhancing solubility and providing additional sites for rapid glucose release. Once glycogen is fully assembled, it can be stored in cytosolic granules or transported into mitochondria for oxidation in muscle cells.

Regulation of glycogenogenesis operates through hormonal and allosteric mechanisms. Insulin activates glycogen synthase by dephosphorylation, promoting glycogen synthesis after a meal. In contrast, glucagon and epinephrine trigger glycogen phosphorylase to degrade glycogen during fasting or stress. Catabolic signals also phosphorylate glycogen synthase through cAMP-dependent protein kinase, reducing its activity. This tightly controlled balance ensures that glycogen stores are replenished when glucose is abundant and mobilized when energy is required.