glykogenu

Glykogen, commonly referred to as glycogen, is a large, branched polysaccharide composed of glucose units linked primarily by α(1→4) glycosidic bonds with occasional α(1→6) branches. It serves as the principal storage form of glucose in animals, plants, and fungi. In mammals, glycogen is predominantly stored in the liver and skeletal muscle tissues. In the liver, it helps maintain blood glucose levels between meals, whereas in muscle it provides a rapidly mobilizable energy reserve during periods of increased activity.

The synthesis of glycogen (glycogenesis) is initiated by the enzyme glycogenin, which autoglycosylates and provides a primer for glycogen synthase to add additional glucose residues. Branching enzyme (glycogen branching enzyme) introduces α(1→6) linkages, creating a highly branched structure that permits efficient addition and removal of glucose units. Glycogenolysis, the degradation process, is carried out by glycogen phosphorylase to release glucose-1-phosphate, and by debranching enzyme to remove branch points.

Regulation of glycogen metabolism is tightly coordinated by hormonal signals. Insulin promotes glycogenesis and inhibits glycogenolysis, whereas glucagon and epinephrine stimulate glycogen breakdown. Intracellular signals such as cyclic AMP and protein kinase A modulate enzyme activities accordingly. Dysregulation can lead to metabolic disorders: for instance, glycogen storage diseases arise from inherited deficiencies in enzymes like glycogen phosphorylase or debranching enzyme, causing abnormal accumulation or inadequate breakdown of glycogen. Understanding glykogen metabolism is essential for interpreting diseases such as diabetes, hypoglycemia, and various glycogen storage disorders.