Question

Suppose a researcher introduces a mutation into the glucosidase domain of the mammalian glycogen debranching enzyme. The mutation inhibits the activity of the glucosidase but does not affect the other functions of the enzyme. The researcher then introduces the mutated enzyme into mammalian cells that do not express wild type glycogen debranching enzyme. Predict the effect of the mutation on glycogen metabolism.

Answer 1

cells will have glycogen molecules with branches of a single glucose residue

Step-by-step explanation:

Glycogen debranching enzymes are proteins that catalyze the removal of branching from glycogen, which is a multibranched polysaccharide composed of glucose units and serves as a form of energy storage. These enzymes have two catalytic activities on a single polypeptide chain: glucosyltransferase and glucosidase activities, which are both required for glycogen breakdown. Glycogen degradation requires both glycogen phosphorylase and glycogen debranching enzymes. First, a glycogen phosphorylase acts to digest a glycogen branch down to four glucose residues. Subsequently, the debranching enzyme through its glucosyltransferase activity acts to transfer three glucose residues to a nearby branch of the glycogen chain. Finally, through its glucosidase activity, the debranching enzyme cleaves the remaining α-1,6 linkage in order to release free glucose.