The inhibition was much weaker than that of PMSF. To confirm that was a serine protease and provide a better estimate of its molecular size, a TAMRA-fluorophosphonate probe was used to conduct activity-based protein profiling of vaginal tissues from Fbln5 heterozygous and knockout mice. FP is an irreversible inhibitor of fluorophosphonate/ fluorophosphate derivatives and preferentially inhibits serine proteases. The reactivity of FP requires the presence of a catalytically active serine hydrolase. Multiple proteases were labeled by FP indicating multiple catalytically active serine proteases in the vaginal wall. Most labeled proteases, however, were similar in KO and Het animals. In contrast, V1 protease was increased in vaginal extracts from KO animals. Based on these results, we performed activity-based pull down assays of V1 protease using a biotinylated FP probe. Consistent with TAMRA-FP probe, upregulation of a,25-kDa FP-reactive band was detected in KO extracts, which was abolished by heat inactivation. The band was excised and sequenced by mass spectrometry. Four sequences were obtained that partially matched to PRSS1-3. Taken together, the biochemistry, inhibitory profile, activity-based protein profiling, and mass spectrometry data suggest that V1 protease is a trypsin-like, but not chymotrypsin-like, serine protease similar to PRSS1-3 trypsinogens. Based on its molecular size, mass spectrometric analysis, resistance to common trypsin inhibitors and iii) optimal pH, we concluded that V1 is most likely PRSS3. PRSS3, together with PRSS1 and PRSS2, comprise a DMXB-A structure trypsinogen family. While PRSS1 and PRSS2 are major pancreatic trypsinogens, PRSS3 is shown to be expressed both in the pancreas and extra-pancreatic tissues, including the brain and skin. To examine if PRSS3 is secreted from vaginal tissues, vagina organ culture was prepared from Ethyl eicosapentaenoate wild-type and Fbln52/2 mice and conditioned media were collected. Western blot analysis of conditioned media showed cross-reactivity to PRSS3 at approximately 25 kDa both in wildtype and knockout mice. PRSS3 levels, however, did not differ. In contrast, 25-kDa caseinolytic activity was increased in conditioned media from Fbln52/2 vagina relative to almost nondetectable activity in wild-type, suggesting the possibili
