Localization of post-proline cleaving peptidases in Tenebrio molitor larval midgut

Two soluble post-proline cleaving peptidase activities, PPCP1 and PPCP2, were demonstrated in Tenebrio molitor larval midgut with the substrate benzyloxycarbonyl- l-alanyl- l-proline p-nitroanilide. Both activities were serine peptidases. PPCP1 was active in acidic buffers, with maximum activity at pH 5.3, and was located mainly in the more acidic anterior midgut lumen. The dynamics of PPCP1 activity and the total activity of soluble digestive peptidases in the course of food digestion were similar, suggesting that the enzyme participates in protein digestion. PPCP2 is a nondigestive soluble tissue enzyme evenly distributed along the midgut. An increase in the activity of PPCP2 was observed in buffers of pH 5.6–8.6 and was maximal at pH 7.4. The sensitivity of PPCP2 to inhibitors and the effect of pH are similar to prolyl oligopeptidases with a cysteine residue near the substrate binding site.