Catalyzes the epimerization of trans-4-hydroxy-L-proline (t4LHyp) to cis-4-hydroxy-D-proline (c4DHyp). Is likely involved in a degradation pathway that converts t4LHyp to alpha-ketoglutarate. Can also catalyze the epimerization of trans-3-hydroxy-L-proline (t3LHyp) to cis-3-hydroxy-D-proline (c3DHyp), albeit with 19-fold lower efficiency. Displays no proline racemase activity