3-(3-hydroxyphenyl)propanoate hydroxylase (, mhpA (gene)) is an enzyme with systematic name 3-(3-hydroxyphenyl)propanoate,NADH:oxygen oxidoreductase (2-hydroxylating). This enzyme catalyses the following chemical reaction
The four substrates of this enzyme are 3-hydroxybenzenepropanoic acid, reduced nicotinamide adenine dinucleotide (NADH), oxygen, and a proton. Its products are 2,3-dihydroxyphenylpropionic acid, oxidised NAD<sup>+</sup>, and water. It is a flavoprotein that uses flavin adenine dinucleotide as a cofactor.
The enzyme can act on related substrates, for example to convert 3'-hydroxycinnamic acid to 2,3-dihydroxycinnamic acid: