In enzymology, a 3-hydroxybutyryl-CoA epimerase (EC 5.1.2.3) is an enzyme that catalyzes the chemical reaction

(S)-3-hydroxybutanoyl-CoA ${\displaystyle \rightleftharpoons }$ (R)-3-hydroxybutanoyl-CoA

Hence, this enzyme has one substrate, (S)-3-hydroxybutanoyl-CoA, and one product, (R)-3-hydroxybutanoyl-CoA.

This enzyme belongs to the family of isomerases, specifically those racemases and epimerases acting on hydroxy acids and derivatives. The systematic name of this enzyme class is 3-hydroxybutanoyl-CoA 3-epimerase. Other names in common use include 3-hydroxybutyryl coenzyme A epimerase, and 3-hydroxyacyl-CoA epimerase. This enzyme participates in fatty acid metabolism and butanoate metabolism.

Structural studies

As of late 2007, four structures have been solved for this class of enzymes, with PDB accession codes 1WDK, 1WDL, 1WDM, and 2D3T.