What is the function of a protein phosphatase?

• A. Adds phosphates to proteins.
• B. Removes phosphates from proteins.
• C. Degrades proteins.
• D. Transports proteins across membranes.

Answer: (B)

Phosphatases catalyze the removal of phosphate groups from proteins, reversing phosphorylation and helping to turn signaling events off or tune their strength. Phosphorylation by kinases often changes a protein’s activity, interactions, or location, so phosphatases reset those changes by hydrolyzing the phosphate bond. Some target serine or threonine residues, others tyrosine residues, reflecting different substrate specificities. This clearly fits the idea that the function is to remove phosphates; adding phosphates is done by kinases, degrading proteins is proteolysis, and transporting proteins across membranes is carried out by transporters.