In enzymology, hydroxyacid-oxoacid transhydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are (S)-3-hydroxybutyric acid and ñ-ketoglutaric acid. Its products are acetoacetic acid and (R)-2-hydroxyglutaric acid.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with other acceptors. The systematic name of this enzyme class is (S)-3-hydroxybutanoate:2-oxoglutarate oxidoreductase. This enzyme is also called transhydrogenase, hydroxy acid-oxo acid.