Dioxygenase that catalyzes the 2-oxoglutarate-dependent selective hydroxylation of free L-proline to cis-4-hydroxy-L-proline (cis-4-Hyp). 2-oxoglutarate + L-proline + O2 = cis-4-hydroxy-L-proline + CO2 + succinate Binds 1 Fe(2+) ion. Inhibited by metal ions such as Co(2+), Zn(2+), Cu(2+) or Ni(2+). Is also inhibited by EDTA or diethylpyrocarbonate (DEPC) in vitro. Unlike the procollagen-proline cis-3- and trans-4-hydroxylases from mammals, does not necessarily require L-ascorbate for activity although it does increase the activity of the enzyme. kcat is 24 sec(-1). Optimum pH is 6.5. Optimum temperature is 25 degrees Celsius. Would be one of the most promising biocatalysts for production of cis-4-hydroxy-L-proline (cis-4-Hyp), a compound which was clinically evaluated as an anticancer drug. Belongs to the L-proline cis-4-/cis-3-hydroxylase family.