Has proline-specific tripeptidyl aminopeptidase and tetrapeptidyl aminopeptidase activity. Activity is highest against tripeptides containing an Ala-Pro motif. Involved in the final processing of transglutaminase, by removing either the tetrapeptide Phe-Arg-Ala-Pro left after TAMEP or SAM-P45 hydrolysis, or the tripeptide Arg-Ala-Pro left after SGMP II hydrolysis in a single step. Completely inhibited by the serine protease inhibitor phenylmethylsulfonyl fluoride. Partially inhibited by the serine protease inhibitor Pefabloc. Not inhibited by cysteine proteinase-specific or metalloproteinase-specific inhibitors. Not inhibited by prolinal or its derivatives. EDTA and EGTA both partially inhibit this enzyme (PubMed:14519127). EDTA has no effect on activity (PubMed:15598885). Optimum pH is 7.0-7.5 (PubMed:14519127). Optimum pH is 6.0-6.5 (PubMed:15598885). Active between pH 4.3 and 8.3. Stable after 12 hours incubation from pH 4.0 to 9.0. Optimum temperature is 45 degrees Celsius. Secreted (PubMed:14519127). Cell surface (PubMed:15598885). Belongs to the peptidase S37 family.