Tryptase is a serine protease secreted by mast cells that is able to activate other cells. In the
present studies we have tested whether these responses could be mediated by thrombin
receptors or PAR-2, two G-protein-coupled receptors that are activated by proteolysis. When
added to a peptide corresponding to the N terminus of PAR-2, tryptase cleaved the peptide
at the activating site, but at higher concentrations it also cleaved downstream, as did trypsin,
a known activator of PAR-2. Thrombin, factor Xa, plasmin, urokinase, plasma kallikrein, and …