Proline 4-hydroxylase: Stereochemical course of the reaction

The stereochemical course of the hydroxylation of (S)-proline by proline 4-hydroxylase from Streptomyces griseoviridus P8648 has been investigated using (2S, 4S)-[4-2H1]-proline and (2S, 4R)-[4-2H1]-proline and found to occur with retention of stereochemistry at C-4 of proline.