Difference Between Lyases and Ligases

Main Difference – Lyases vs Ligases

Lyases and ligases are types of enzymes that can catalyze certain biochemical reactions. Lyases catalyze reactions that involve bond breaking. Lyases are also called synthases. Ligases are involved in catalyzing some biochemical reactions that result in bond forming. Ligases are also called synthetases. There is a significant difference between lyases and ligases based on their functions in biological systems. The main difference between lyases and ligases is that lyases break chemical bonds in order to form new compounds whereas ligases form chemical bonds in order to combine different compounds.

Key Areas Covered

1. What are Lyases
      – Definition, Properties, and Functions
2. What are Ligases
      – Definition, Properties, and Functions
3. What is the Difference Between Lyases and Ligases
      – Comparison of Key Differences

Key Terms: Enzymes, Catalysts, Ligases, Lyases, Synthases, Synthetases

What are Lyases

Lyases are enzymes that catalyze bond-breaking reactions. Therefore, a lyase will catalyze the cleavage of a certain molecule. The bond breaking occurs in the form of an elimination reaction. Therefore, the resulting product will have a double bond due to the elimination of atoms. However, this bond breaking does not occur through hydrolysis or oxidation.

Since it is an elimination reaction, only one substrate is involved in the reaction as the reactant. Two molecules are given as end products. One molecule is the substrate with the double bond. The other one is the eliminated molecule. The reverse reaction is also possible in this kind of reactions. But lyases need two reactants for the reverse reaction – the molecule with the double bond and the small molecule that is going to be added to the double bond.

Reactions catalyzed by lyases are commonly found in glycolysis and Krebs cycle. For example, in glycolysis, lyases form glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) from fructose 1,6-bisphosphate (F 1,6-BP).

Figure 1: Use of Lyase Enzyme in Glycolysis

Deficiency of lyases causes a disease in our body. This is called lyase deficiency disorder. However, it is a rare inherited disorder. This disorder prevents our body from processing the amino acid leucine.

What are Ligases

Ligases are a class of enzymes that are involved in catalyzing bond formation reactions. Therefore, these enzymes catalyze the formation of compounds that are larger than their starting material or different compounds. The reactions occur through hydrolysis of a small group in order to form a large group, or through the combination of two different molecules.

Ligases are sometimes called synthetases. This is because ligases are used to produce new molecules. There are about 50 different enzymes in this class. The reactions catalyzed by ligases require chemical energy from Adenosine Triphosphate (ATP) molecules. Here, the ATP is converted into ADP (Adenosine Diphosphate).

Figure 2: Ligation of DNA Fragments is catalyzed by DNA Ligase Enzyme

For example, DNA ligase enzyme is capable of closing the breaks in DNA molecules. In DNA replication process, DNA ligases are useful in joining the complementary DNA fragments. Due to this reason, ligases are sometimes called molecular glue.

Difference Between Lyases and Ligases

Definition

Lyases: Lyases are enzymes that catalyze bond breaking reactions.

Ligases: Ligases are a class of enzymes that are involved in catalyzing bond formation reactions.

Effect on Chemical Bonds

Lyases: Lyases cause the forming of double bonds.

Ligases: Ligases cause the forming of chemical bonds.

Reaction Type

Lyases: Lyases are involved in elimination reactions.

Ligases: Ligases are involved in hydrolysis reactions.

Reactants

Lyases: Lyases act on a single substrate per reaction.

Ligases: ligases act on two substrates or reactants per reaction.

Applications

Lyases: Lyases are useful in glycolysis.

Ligases: Ligases are important in DNA replication.

Conclusion

Lyases and ligases are enzymes involved in catalyzing biochemical reactions. Lyases and ligases are different from each other according to their functions in biological systems. The main difference between lyases and ligases is that lyases break chemical bonds in order to form new compounds whereas ligases form chemical bonds in order to combine different compounds.

References:

1. “Ligase.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 12 Aug. 2010, Available here. Accessed 13 Sept. 2017.
2. “Ligase.” Wikipedia, Wikimedia Foundation, 11 Sept. 2017, Available here. Accessed 13 Sept. 2017.
3. “Lyases.” Lyases – an overview | ScienceDirect Topics, Available here. Accessed 13 Sept. 2017.

Image Courtesy:

1. “Lyasesexample” By Melowdeeh at English Wikibooks – Transferred from en.wikibooks to Commons. (Public Domain) via Commons Wikimedia
2. “Ligation” By Madprime – Own work (CC BY-SA 3.0) via Commons Wikimedia