Dipeptidyl peptidase that cleaves off N-terminal dipeptides from proteins having a Pro or Ala residue at position 2 (PubMed:12662155, PubMed:16475979, PubMed:19667070, PubMed:29382749, PubMed:30291141, PubMed:33731929). Acts as a key inhibitor of caspase-1-dependent monocyte and macrophage pyroptosis in resting cells by preventing activation of NLRP1 and CARD8 (PubMed:27820798, PubMed:29967349, PubMed:30291141, PubMed:31525884, PubMed:32796818). Sequesters the cleaved C-terminal part of NLRP1 and CARD8, which respectively constitute the active part of the NLRP1 and CARD8 inflammasomes, in a ternary complex, thereby preventing their oligomerization and activation (PubMed:34019797, PubMed:33731929, PubMed:33731932). The dipeptidyl peptidase activity is required to suppress NLRP1 and CARD8; however, neither NLRP1 nor CARD8 are bona fide substrates of DPP9, suggesting the existence of substrate(s) required for NLRP1 and CARD8 inhibition (PubMed:33731929). Release of an N-terminal dipeptide, Xaa-Yaa-|-Zaa-, from a polypeptide, preferentially when Yaa is Pro, provided Zaa is neither Pro nor hydroxyproline. Inhibited by the serine proteinase inhibitor 4-(2-aminoethyl)benzenesulphonyl fluoride (AEBSF), and by di-isopropylfluorophosphate (PubMed:12662155). Inhibited by Val-boroPro (Talabostat, PT-100), a non-selective inhibitor, which triggers pyroptosis in monocytes and macrophages (PubMed:27820798, PubMed:29967349, PubMed:32796818, PubMed:33731932). Val-boroPro inhibits activity by binding to the active site, mimicking a substrate-bound state, thereby displacing the C-terminal fragment of NLRP1, leading to activation of the NLRP1 inflammasome (PubMed:34019797, PubMed:33731932). In contrast, Val-boroPro does not directly displaces CARD8: it acts by promoting degradation of the N-terminal part of CARD8, leading to indirect disruption of the ternary complex (PubMed:34019797). kcat is 121 sec(-1) with Gly-Pro-AMC substrate (PubMed:29382749). kcat is 52,6 sec(-1) with Lys-Pro-AMC substrate (PubMed:29382749). kcat is 54 sec(-1) with Asp-Pro-AMC substrate (PubMed:29382749). kcat is 40,3 sec(-1) with Trp-Pro-AMC substrate (PubMed:29382749). kcat is 79,9 sec(-1) with Val-Pro-AMC substrate (PubMed:29382749). Optimum pH is 7.5-8.5. Little activity below pH 6.5. Homodimer (PubMed:16475979, PubMed:29382749). Forms a ternary complex with NLRP1, composed of a DPP9 homodimer, one full-length NLRP1 protein, and one cleaved C-terminus of NLRP1 (NACHT, LRR and PYD domains-containing protein 1, C-terminus) (PubMed:33731929, PubMed:33731932). Forms a ternary complex with CARD8, composed of a DPP9 homodimer, one full-length NLRP1 protein, and one cleaved C-terminus of CARD8 (Caspase recruitment domain-containing protein 8, C-terminus) (PubMed:33731929, PubMed:34019797). In the ternary complex, only one subunit of the DPP9 homodimer is bound to NLRP1 or CARD8 (PubMed:34019797, PubMed:33731932). Ubiquitously expressed, with highest levels in liver, heart and muscle, and lowest levels in brain. Active peptidase. Contains a nuclear localization signal at positions 2-9. Belongs to the peptidase S9B family. DPPIV subfamily. Truncated N-terminus. Truncated N-terminus. Extended N-terminus. Truncated N-terminus. Truncated N-terminus. Probable cloning artifact. Aberrant splicing.