Proline 3-hydroxylase () is an enzyme that catalyzes the chemical reaction:
The systematic name of this enzyme class is L-proline,2-oxoglutarate:oxygen oxidoreductase (3-hydroxylating). This enzyme is also called P-3-H. It is an oxidase which uses molecular oxygen as oxidant, with incorporation of one of its atoms. These enzymes are non-heme iron proteins with ferryl active site where Fe(IV)=O is the species that transfers its oxygen to the substrate.
The mechanism used by these 2-oxoglutarate-dependent oxygenases requires 2-oxoglutaric acid to activate the iron oxygen complex, and this gives succinic acid and carbon dioxide when the second atom of the molecular oxygen is removed.