Which enzyme category uses ATP in its reaction?

• A. Ligase
• B. Lyase
• C. Isomerase
• D. Transferase

Answer: (A)

Ligases use energy from ATP to form new bonds between substrates, making ATP hydrolysis the driving force behind the reaction. This energy coupling is the hallmark of this class: the substrate pair is joined while ATP is converted to ADP and phosphate (or AMP and PPi), providing the push needed to create the new bond. Examples include DNA ligase, which seals nicks in the sugar-phosphate backbone during replication, and aminoacyl-tRNA synthetases, which activate amino acids by forming aminoacyl-AMP before charging tRNA.

Lyases, isomerases, and transferases operate differently: lyases cleave or form bonds without requiring ATP, isomerases rearrange atoms within a molecule without ATP, and transferases move functional groups between molecules (some transferases, like kinases, use ATP to transfer a phosphate group, but their defining role isn’t bond formation driven by ATP in the same way as ligases). Therefore, the enzyme category that uses ATP in its reaction to drive bond formation is ligases.