Question

Describe the roles of glycogen phosphorylase, debranching enzyme, and glucose 6-phosphatase in glycogen breakdown, and predict the biochemical and potential clinical consequences in deficiencies in these enzymes

Answer 1

Glycogen phosphorylase breaks down glycogen by removing glucose units. Debranching enzyme removes the remaining glucose units near the branching point. Glucose 6-phosphatase releases free glucose from the remaining glucose residue.

Step-by-step explanation:

Glycogen phosphorylase is the key enzyme in glycogen breakdown. It acts on a-1→4 glycosidic linkages to release glucose units from the linear chain. Debranching enzyme (amylo-1,6-glycosi-dase) removes the remaining three glucose units near the branching point, leaving one glucose residue linked with a-1→6 glycosidic linkage, which is then acted upon by glucose 6-phosphatase to release free glucose.

Deficiencies in these enzymes can have biochemical and clinical consequences. Deficiency in glycogen phosphorylase can lead to glycogen storage diseases (GSDs) in which the breakdown of glycogen is impaired. Deficiency in debranching enzyme can cause GSD type III, resulting in accumulation of abnormal glycogen. Deficiency in glucose 6-phosphatase can lead to GSD type I, known as von Gierke disease, resulting in hypoglycemia and other metabolic abnormalities.