Releases the N-terminal proline from various substrates. Has a high specificity towards di- or tripeptides with proline at the NH(2)-terminal position, but is not able to hydrolyze longer peptides, or peptides with hydroxyproline at the NH(2)-end. Partially hydrolyzes also peptides with alanine, glycine and leucine at the NH(2)-terminal position. Release of N-terminal proline from a peptide. Inhibited strongly by 3,4-dichloroisocoumarin, bestatin and heavy metal ions. Inactivated by p-chloromercuribenzoate, but reactivated by dithiothreitol. Optimum pH is 6-7. Stable at temperatures below 40 degrees Celsius. Homotrimer. Belongs to the peptidase S33 family.