Properties of post-proline cleaving enzymes from Tenebrio molitor

Two post-proline cleaving peptidases PPCP1 and PPCP2 with molecular masses of 101 and 63 kDa, respectively, hydrolyzing Z-AlaAlaPro-pNA were isolated for the first time from the larval midgut of the yellow mealworm Tenebrio molitor and characterized. PPCP1 was active only in acidic media, with a maximum at pH 5.6, whereas PPCP2, both in acidic and alkaline media with a maximum at pH 7.9. Using inhibitory analysis, both PPCP1 and PPCP2 were shown to belong to serine peptidases. The data obtained indicate that a Cys residue is located close to the PPCP2 substrate binding site. Z-Pro-prolinal, a specific inhibitor of prolyl oligopeptidases, completely inhibited PPCP2 and partially PPCP1. The substrate specificities of the isolated enzymes were studied. Z-Ala-Ala-Pro-pNA was the best substrate for PPCP1, and Z-Ala-Pro-pNA, for PPCP2. The combination of the properties allows characterization of PPCP2 as a proplyl oligopeptidase.