Storage and release of MC proteases. Mast cell (MC) proteases are synthesized as preproenzymes where both the signal (pre-) and activation (pro-) peptides are cleaved off intracellularly, a process in which dipeptidyl peptidase I/cathepsin C has a key role.13 Hence, enzymatically active proteases are stored in the MC granule. Major MC tryptases are tetrameric enzymes, whereas chymases and mast cell carboxypeptidase A (MC-CPA) are monomeric. Notably, for many MC proteases, the storage is strongly dependent on electrostatic interaction with serglycin proteoglycan, whereas others are stored independently of serglycin. After MC degranulation, MC proteases are released in complexes with serglycin. At exposure to extracellular pH, MC proteases may either be dissociated from serglycin or remain associated.
