Tryptase is the major neutral protease present in mast cells and is secreted upon the coupled activation-degranulation response of this cell type. Plays a role in innate immunity. Preferential cleavage: Arg-|-Xaa, Lys-|-Xaa, but with more restricted specificity than trypsin. Homotetramer. The active tetramer is converted to inactive monomers at neutral and acidic pH in the absence of heparin. Low concentrations of inactive monomers become active monomers at pH 6.0 in the presence of heparin. When the concentration of active monomers is higher, they convert to active monomers and then to active tetramers. These monomers are active and functionally distinct from the tetrameric enzyme. In contrast to the hidden active sites in the tetrameric form, the active site of the monomeric form is accessible for macromolecular proteins and inhibitors eg: fibrinogen which is a substrate for the monomeric but not for the tetrameric form. The monomeric form forms a complex with SERPINB6 (By similarity). Released from the secretory granules upon mast cell activation. During embryogenesis, detected primarily in skin. Not detected at early embryonic stages but is abundantly expressed in later stages with a peak at 17.5 dpc-18.5 dpc. Mutant mice do not exhibit any visible phenotype when maintained in pathogen-free facilities. However, after peritoneal inoculation of Klebsiella pneumoniae, they cannot efficiently fight the infection and show increased lethality. Probably non functional. Belongs to the peptidase S1 family. Tryptase subfamily.