Serine protease inhibitor which exhibits antifibrinolytic, antielastolytic and antimicrobial activities (PubMed:27208884). Displays antimicrobial activity against bacteria and fungi (PubMed:27208884). Likely functions in the innate immune response to microbial infection and possibly in the venom, as an antifibrinolytic agent (PubMed:27208884). The recombinant form inhibits trypsin (IC(50)=80.02 nM, Ki=127.25 nM), chymotrypsin (IC(50)=393.78 nM, Ki=432.59 nM), the microbial serine proteases subtilisin A (IC(50)=379.20 nM, Ki=492.77 nM) and proteinase K (IC(50)=189.43 nM, Ki=271.76 nM), plasmin (IC(50)=457.98 nM, Ki=502.91 nM), human elastase (IC(50)=347.81 nM, Ki=469.90 nM) and porcine elastase (IC(50)=94.70 nM, Ki=125.62 nM) (PubMed:27208884). Does not inhibit thrombin (PubMed:27208884). Binds to human plasmin and inhibits the plasmin-mediated degradation of fibrin to fibrin degradation products (PubMed:27208884). Also binds to bacterial and fungal surfaces and exhibits antimicrobial activity against the Gram-positive bacteria B.thuringiensis (MIC=4.21 uM) and P.larvae (MIC=11.13 uM), the Gram-negative bacterium E.coli (MIC=6.50 uM), and the fungus B.bassiana (IC(50)=2.57 uM) (PubMed:27208884). The synthetic peptide also exhibits antimicrobial activity against the Gram-positive bacterium P.larvae (MIC=41.12 uM), the Gram-negative bacterium P.aeruginosa (MIC=65.75 uM), and the fungus B.bassiana (IC(50)=44.27 uM) (Ref.2). In vitro it does not induce an inflammatory response and has no cytotoxic activity against mouse embryo cells (Ref.2). Antibacterial activity against P.aeruginosa is retained between 25 and 90 degrees Celsius. Expressed in the epidermis, fat body and venom gland. Up-regulated in the fat body after injection with bacteria (B.thuringiensis, P.larvae or E.coli) or the fungus B.bassiana. Belongs to the secapin family.