Which of the following is an example of ligases enzyme?

Carboxylases

The correct answer is option 3. Carboxylases.

Sure! Let’s dive into each enzyme type and explain why **carboxylases** are examples of ligase enzymes:

1. Racemases

Racemases are isomerases that catalyze the conversion of one enantiomer of a chiral molecule into its mirror image. This involves the inversion of configuration around a single chiral center but does not involve the formation of new bonds. Alanine racemase converts L-alanine to D-alanine.

2. Mutases

Mutases are isomerases that catalyze the transfer of a functional group from one position to another within the same molecule. This type of reaction changes the position of a functional group but does not involve bond formation between different molecules. Phosphoglycerate mutase catalyzes the transfer of a phosphate group within 3-phosphoglycerate to form 2-phosphoglycerate.

3. Carboxylases

Carboxylases are enzymes that add a carboxyl group (\(-COOH\)) to a substrate. This reaction often requires energy, which is typically derived from ATP (adenosine triphosphate).

Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate by adding a carboxyl group. This reaction is crucial in gluconeogenesis and the citric acid cycle.

\(\text{Pyruvate} + \text{CO}_2 + \text{ATP} \rightarrow \text{Oxaloacetate} + \text{ADP} + \text{P}_i \)

In this reaction, the carboxyl group is added to the substrate, and ATP is used as an energy source, characteristic of ligase activity.

4. Epimerases

Epimerases are isomerases that catalyze the conversion of one epimer (a specific type of stereoisomer differing in configuration at one chiral center) into another. This involves a change in the configuration around a single chiral center. UDP-glucose 4-epimerase converts UDP-glucose to UDP-galactose.

Summary:

Carboxylases are ligases because they catalyze reactions where a carboxyl group is added to a substrate, and this process requires energy, typically from ATP.

Racemases, mutases, and epimerases are isomerases that rearrange or convert molecules without forming new bonds between different molecules. They do not utilize ATP to drive their reactions.

Thus, among the options provided, carboxylases are the correct example of ligase enzymes.