Interaction of human low molecular weight kininogen with human mast cell tryptase

The capacity of purified tryptase, the major neutral tryptic protease of human lung mast cells, to serve as a kininogenase was examined with purified human low molecular weight kininogen (LMWK) as the substrate. Incubating of 25 mug of tryptase with LMWK for 2 to 30 minutes, with or without heparin, yielded no net time-dependent kinin release as determined on the estrous rat uterus. The 0.4 mug of kinin seen represented less than 10% of that released from excess LMWK by 5 mug of human urinary kallikrein in 5 min. Incubation at pH 5.5 with or without heparin did not significantly alter this result. LMWK did not appear by SDS-PAGE to be cleaved by tryptase either in the presence or absence of heparin. In contrast to its action on HMWK, tryptase did not extensively cleave LMWK, or destroy its reactivity with kallikrein.