Debranchingentsyymi

Debranchingentsyymi is a cytosolic enzyme involved in the breakdown of glycogen and other branched glucose polymers. It functions as part of the glycogenolysis pathway, acting after glycogen phosphorylase has removed many glucose units from the ends of chains. Its action allows complete proteolysis of branched structures rather than leaving inaccessible limit branches.

The enzyme carries two coordinated activities. First, a transferase activity (4-α-glucanotransferase) shifts a short chain of glucose residues from a branched point to a nearby linear chain. Second, a glucosidase activity (amylo-1,6-glucosidase) hydrolyzes the remaining α-1,6-glycosidic bond at the branch point to release a free glucose molecule. Together, these activities prevent accumulation of limit dextrins and enable continued glycogen degradation.

Genetics and distribution: In humans, the debranching enzyme is encoded by the AGL gene and is found in various tissues, notably liver and muscle. The enzyme is conserved across many eukaryotes and some bacteria, reflecting its essential role in carbohydrate metabolism.

Clinical relevance: Deficiency of debranching functionality leads to glycogen storage disease type III, also called Cori disease. Patients may exhibit hepatomegaly, hypoglycemia, growth delays, and abnormal glycogen structure characterized by limit dextrin-like remnants. Management is supportive and aimed at maintaining metabolic stability.

Structure and regulation: Debranchingentsyymi comprises domains corresponding to its transferase and glucosidase activities within a single polypeptide in humans. Its activity is integrated into the broader regulatory network of glycogenolysis, cooperating with glycogen phosphorylase and other enzymes to control glucose release in response to metabolic signals.