Catalyzes the epimerization of trans-4-hydroxy-L-proline (t4LHyp) to cis-4-hydroxy-D-proline (c4DHyp). May be involved in a degradation pathway of t4LHyp. Can also catalyze the epimerization of trans-3-hydroxy-L-proline (t3LHyp) to cis-3-hydroxy-D-proline (c3DHyp) in vitro. Displays no proline racemase activity. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline Belongs to the proline racemase family.