What is the Difference Between Branching and Debranching Enzyme

The main difference between branching and debranching enzyme is that branching enzyme adds branches to the growing glycogen during the glycogen synthesis, whereas debranching enzyme facilitates the breakdown of glycogen mobilizing glucose.

Branching and debranching enzymes are the two types of enzymes responsible for the formation and breakdown of glycogen in the body.   

Key Areas Covered

1. What is a Branching Enzyme
     – Definition, Structure, Function
2. What is a Debranching Enzyme
     – Definition, Structure, Function
3. Similarities Between Branching and Debranching Enzyme
     – Outline of Common Features
4. Difference Between Branching and Debranching Enzyme
     – Comparison of Key Differences

Key Terms

Branching Enzyme, Debranching Enzyme

What is Branching Enzyme

The branching enzyme is the enzyme responsible for the addition of branches in the growing glycogen molecules. Other names for branching enzymes include 1,4-alpha-glucan-branching enzyme and glycogen branching enzyme. GBE1 is the gene that encodes the branching enzyme. Glycogen is also the storage form of glucose. During the synthesis of glycogen, glucose 1-phosphate reacts with uridine triphosphate (UTP), forming the active form of glucose, UDP-glucose. Glycogen synthase catalyzes the reaction of forming α-1,4-glycosidic linkage by transferring the activated glycosyl unit of UDP-glucose to the hydroxyl group at the C-4 of a terminal residue of glycogen. However, the glycogen branching enzyme is responsible for the formation of branches in the glycogen molecule. The branching of glycogen increases the solubility of glycogen and decreases the osmotic strength of the molecule.

Figure 1: Glycogen Branching Enzyme

Furthermore, the branching enzyme forms branches in the glycogen molecule by catalyzing the transfer of alpha-1,4-linked glucosyl units from the outer end to an alpha-1,6 position of the same or the neighboring glycogen chain. Apart from that, a higher concentration of branching enzymes occurs in the liver and muscles. Mutations in the branching enzyme gene cause a disease called Andersen’s disease.

What is Debranching Enzyme

The debranching enzyme is the enzyme that facilitates the breakdown of glycogen, forming a store of glucose in the body. This enzyme breaks down the glycogen deposits in the liver and muscles, constituting the major source of energy reserves in the body. In addition, the breakdown of glycogen is a highly regulated process in the liver and muscles controlled by the hormones glucagon and insulin. In mammals, yeast, and some bacteria, the debranching enzyme performs both glucosyltransferase and glucosidase activity. When the two functions are carried out by separate enzymes, the debranching enzyme refers to the glucosidase enzyme.

Figure 2: Function of the Debranching Enzyme

Moreover, along with the phosphorylase enzyme, the main function of the debranching enzyme is to break down glycogen and the mobilization of glucose. Phosphorylase cleaves α-1,4- glycosidic bond between two adjacent glucose molecules. However, glucose branches occur as α-1,6 linkages. Here, the debranching enzyme performs two functions: 4-α-D-glucanotransferase and amylo-α-1,6-glucosidase. First is the glucosyltransferase activity, transferring three glucose residues from branches with four glucose residues, and the second is the glucosidase activity, cleaving the remaining α -1,6-linkage. Mutations in the debranching enzyme can also cause a metabolic disease called Glycogen storage disease type III.

Similarities Between Branching and Debranching Enzyme

• Branching and debranching enzymes are two types of enzymes responsible for the formation and breakdown of glycogen.
• They work on deposits of glycogen in the liver and muscles.

Difference Between Branching and Debranching Enzyme

Definition

Branching enzyme refers to the enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen, a storage form of glucose. Meanwhile, debranching enzyme refers to a molecule that helps facilitate the breakdown of glycogen, which serves as a store of glucose in the body.

Function

The main function of the branching enzyme is to add branches to the growing glycogen molecules, while the main function of the debranching enzyme is to facilitate the breakdown of glycogen, mobilizing glucose.

Importance

Branching enzymes synthesize glycogen, while debranching enzymes break down glycogen.

Domains

Branching enzymes contain CBM_48—Alpha-amylase domain architecture, while debranching enzymes contain CBM_48—Alpha-amylase or hGDE_N—hGDE-amylase-hGDE—hGDE-central—GDE_C architecture.

Conclusion

In brief, the branching and debranching enzymes are two types of enzymes involved in the synthesis and breakdown of glycogen. They occur in the liver and muscles, where glycogen reserves occur. The branching enzyme is responsible for the synthesis of branches during the synthesis of glycogen. Therefore, it involves the synthesis of glycogen. In comparison, the debranching enzyme is responsible for the breakdown of glycogen mobilizing glucose. Hence, the main difference between branching and debranching enzymes is the function of the enzyme.

References:

1. Glycogen Branching enzyme. Wikipedia. Wikimedia Foundation.  
2. Glycogen Debranching enzyme. Wikipedia. Wikimedia Foundation.

Image Courtesy:

1. “E. Coli Glycogen Branching Enzyme” By Omaryaghi2 – Own work (CC-BY SA 3.0) via Commons Wikimedia
2. “Function and Structure of Eukaryotic Glycogen Debranching Enzyme.” By XiangSong – Own Work (CC-BY SA 4.0) via Commons Wikimedia