Endopeptidase with selective post-Arg cleavage site (PubMed:4197814, PubMed:4197815, PubMed:10066809, PubMed:7981662). Activates prophenoloxidase (PubMed:4197814, PubMed:4197815). Has a probable role in the melanization process as part of the innate immune response (Probable). Stabilized by calcium (PubMed:4197814). Inhibited by di-isopropyl phosphorofluoridate (DFP), phenylmethanesulfonylfluoride (PMSF), p-nitrophenyl-p'-guanidinobenzonate (p-NPGB), p-chloromercuribenzoate (PCMB), ethylenediaminetetraacetic acid (EDTA), urea and CI-13c (PubMed:4197814, PubMed:4197815, PubMed:7981662). Optimum pH is 6.0-8.5. Optimum temperature is 0-25 degrees Celsius. In the active form, heterodimer of a light chain and a heavy chain; disulfide-linked. Expressed in eggs and larval cuticles (at protein level) (PubMed:10066809, PubMed:4197814, PubMed:4197815, PubMed:7981662). Expressed in larval hemocytes and salivary glands (PubMed:10066809). The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. Proteolytically cleaved for activation (PubMed:10066809). Cleavage produces a light chain and a catalytic heavy chain which remains covalently associated probably through an interchain disulfide bond (Probable). Glycosylated. Belongs to the peptidase S1 family. CLIP subfamily.