Releases the N-terminal proline from various substrates. Cleaves Pro-betaNA (L-prolyl-beta-naphthylamide) effectively. Release of N-terminal proline from a peptide. Inhibited by 3,4-DCI, but no significant effect on enzyme activity by pepstatin A, E-64, 1,10-phenanthroline or EDTA. Homotrimer. Belongs to the peptidase S33 family.