Figure 1. The reactions catalyzed by proline racemase (ProR), 4R-hydroxyproline 2-epimerase (4HypE), and trans-3-hydroxy-L-proline dehydratase (t3HypD) and the metabolic pathways in which they participate.
cHyp oxidase, Pyr4H2C deaminase, α-KGSA dehydrogenase, and Δ1-Pyr2C reductase belong to the D-amino acid oxidase (DAAO), dihydrodipicolinate synthase (DHDPS), aldehyde dehydrogenase, and ornithine cyclodeaminase (OCD) (or malate/L-lactate dehydrogenase 2 [MLD2]) superfamilies, respectively. Abbreviations: L-Pro: L-proline; D-Pro: D-proline; 5-AV: 5-aminovalerate; t4Hyp: trans-4-hydroxy-L-proline; c4Hyp: cis-4-hydroxy-D-proline; Pyr4H2C: Δ1-pyrroline 4-hydroxy 2-carboxylate; α-KGSA: α-ketoglutarate semialdehyde; α-KG: α-ketoglutarate; t3Hyp: trans-3-hyroxy-L-proline; Δ2-Pyr2C: Δ2-pyrroline 2-carboxylate; Δ1-Pyr2C: Δ1-pyrroline 2-carboxylate.