HUMAN TRYPTASE FIBRINOGENOLYSIS IS OPTIMAL AT ACIDIC PH AND GENERATESANTICOAGULANT FRAGMENTS IN THE PRESENCE OF THE ANTI-TRYPTASE MONOCLONAL-ANTIBODY B12

Human tryptase is uniquely regulated by its association with heparin a nti resists inhibition by biological protease inhibitors, The effects of pH and B12, an IgG anti-tryptase mAb, on cleavage of the synthetic substrate tosyl-Gly-Pro-Lys-p-nitroanilide and of the biological subst rate fibrinogen by tryptase were examined. Tosyl-Gly-Pro-Lys-p-nitroan ilide cleavage was optimal at neutral pH and was inhibited by the B12 mAb at acidic and neutral pH values, At pH 7.5, inhibition was reversi ble and noncompetitive. In contrast, the optimal pH for tryptase to cl eave fibrinogen was acidic. B12 dramatically enhanced the rate and ext ent that tryptase cleaved all three fibrinogen subunits at pH 6.0 to 6 .5, but inhibited these activities at neutral pH. Major fibrinogen cle avage fragments generated at acidic pH by the B12:tryptase complex wer e identical with those made by plasmin. Thus, at acid pH, tryptase alo ne destroyed the ability of fibrinogen to clot, while the B12:tryptase complex increased the rate of fibrinogenolysis and also generated the anticoagulant, fragment D. The acidic pH optimum for tryptase fibrino genolysis may direct this activity to tissue sites oi inflammation, A putative biological equivalent to B12 would limit tryptase fibrinogeno lytic activity at sites of neutral pH, such as blood, but would augmen t activity at acidic sites.