Releases the N-terminal proline from various substrates including at least dipeptides Pro-Pro, Pro-Gln, Pro-Trp and Pro-Tyr. Acts also on amides (Pro-beta NA) and oligopeptides including Pro-Leu-GlyNH2, Pro-Leu-Gly, Pro-Phe-Gly-Lys, Pro-Pro-Ala-OBut and Pro-Pro-Gly-(Pro-Pro-Gly)(4). Higher activity toward small peptides (up to three residues), but very low activity for longer peptides. Has no activity against p-nitrophenyl acetate, poly_L-proline, Met-Pro or amino acyl amides other than Pro-betaNA (Pyr-betaNA, Phe-betaNA, Cys-betaNA, Met-betaNA, Leu-betaNA, Ala-betaNA and Z-Gly-Pro-betaNA). Release of N-terminal proline from a peptide. Completely inhibited by p-chloromercuribenzoate (PCMB) and heavy metal salts. Partially inhibited by proline and proline derivatives with proline as the amino terminus. Enzyme inactivated by PCMB is reactivated by incubation with 2-mercaptoethanol. Optimum pH is 8.0. Stable at pH 5.5-7.5. Most active at 7.3 with Pro-beta-naphthylamide (Pro-2-NNap) as the substrate. More than 85% of the activity remains between pH 6.5 and 7.5 after incubation for 15 minutes at 30 degrees Celsius and it retains 50% of the original activity after incubation at pH 7.0 and at 30 degrees Celsius for 30 minutes. 50% of the activity remains after 15 minutes preincubations at pH 8.0. Maximum activity at 40 degrees Celsius. Stable at temperatures up to 38 degrees Celsius. Monomer. Belongs to the peptidase S33 family.