In enzymology, a protein-serine epimerase (EC 5.1.1.16) is an enzyme that catalyzes the chemical reaction [protein]-L-serine [protein]-D-serine Hence, this enzyme has one substrate, [protein]-L-serine, and one product, [protein]-D-serine. This enzyme belongs to the family of isomerases, specifically those racemases and epimerases acting on amino acids and derivatives. The systematic name of this enzyme class is [protein]-serine epimerase. This enzyme is also called protein-serine racemase.