Which enzyme does not break bonds to add a phosphate group?

• A. Phosphatase
• B. Phosphorylase
• C. Ligase
• D. Kinase

Answer: (D)

Phosphorylation is carried out by kinases, which transfer a phosphate from ATP to a substrate, attaching the phosphate while leaving the substrate’s other bonds intact. In this process the substrate is phosphorylated without breaking its own bonds, though the ATP’s high-energy phosphoanhydride bond is cleaved to release the phosphate. By contrast, phosphatases remove phosphate groups by hydrolysis, breaking a bond to release phosphate. Phosphorylases add phosphate groups but do so through phosphorolysis, which cleaves a bond in the substrate as the phosphate is added. Ligases build new bonds between molecules, using energy from ATP, but not primarily by adding a phosphate to the same substrate. Therefore, the enzyme that does not break bonds to add a phosphate group is the kinase.