Catalyzes the reversible epimerization of cis-4-hydroxy-D-proline (c4DHyp) to trans-4-hydroxy-L-proline (t4LHyp). May be involved in a degradation pathway that allows P.putida strain KT2440 to grow on either epimer of 4-hydroxyproline, c4DHyp and t4LHyp, as the sole carbon and nitrogen source. Does not exhibit measureable racemase activity in vitro with any of the 19 natural chiral amino acid enantiomers. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline kcat is 69.63 sec(-1) for c4DHyp epimerization. kcat is 7.74 sec(-1) for t4LHyp epimerization. Belongs to the proline racemase family.