Biochemistry, Glycogenesis

Glycogen, the principal storage form of glucose and primary source of non-oxidative glucose for skeletal muscle and liver, confers significant contributions via its degradation by maintaining normal blood glucose levels and providing fuel for muscle contraction. In terms of cytosolic degradation, the major enzymes participating in glycogen breakdown constitute glycogen phosphorylase and debranching enzyme. Glycogen phosphorylase takes care of breaking down linear chain bonds, whereas debranching enzyme transfers glucose residues to the linear chain as to degrade branches. Both enzymes work in skeletal muscle and liver. Because skeletal muscle can utilize the phosphorylated form of glucose as fuel, it does not require glucose-6-phosphatase. On the other hand, the liver requires glucose-6-phosphatase to dephosphorylate glucose and export glucose outside the cell. In terms of lysosomal degradation, acid alpha-glucosidase is responsible for glycogenolysis. Deficiency in any of these enzymes manifests as unique disease states. Most cytosolic degradations alterations effectuate in glycogen storage diseases, including von Gierke disease, Cori disease, and Hers disease. A defect in lysosomal degradation can lead to Pompe disease. The impaired role of glycogenolysis in neural functioning appears via the presentation of Lafora disease. Detection of glycogenolysis alterations can be done mainly through DNA analysis and electron microscopy through the liver and skeletal muscle biopsies.