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The kininogenase activity of human mast cell tryptase.

Tryptase is a tetrameric serine protease [l] which is present almost exclusively in the secretory granules of mast cells [2]. There has been some controversy over the extent to which tryptase may contribute to the generation of kinins which has been reported following mast cell activation [3,4]. Earlier studies suggested that tryptase does not generate bradykinin from either low molecular weight kininogen (LMWK) [5] or high molecular weight kininogen (HMWK) [6]. In contrast Proud [7] in seeking to purify the kallikrein-like enzyme from mast cells found that tryptase and kininogenase activities co-chromatographed, and concluded that tryptase may be the enzyme in mast cells responsible for kinin generation. However, tryptase-induced release of bradykinin from LMWK was optimal at pH 5.5, and the activity was relatively low at neutral pH casting doubt on its biological significance. We have re-examined this issue and have investigated the potential of tryptase to cleave the synthetic chromogenic substrates for kallikreins S2266, S-2302 (both Kabi-Vitrum) and CH-848 (Ferring), and the natural substrates LMWK and HMWK. Tryptase was purified from human lung tissue using high salt extraction, octyl agarose and heparin agarose column chromatography as described previously [8]. Antisera specific for urinary kallikrein did not cross-react with the tryptase on Ouchterolony immunodiffusion. Peptide CH-848 was prepared by solution peptide synthesis [9] using a (7+2) fragment coupling strategy. Heptapeptide Ac-Arg-Pro-ProGly-Phe-Ser-Pro-OH previously synthesised by S.P.P.S. [ 101 and dipeptide H-Phe-Arg. PNA.2HCl were coupled by the BOP activation method, and CH-848 purified by reversed phase MPLC. HMWK was purified from plasma by sequential application of DEAE-Sephadex and CMSephadex, and LMWK using DEAE-Sephadex, CMSephadex and Q-Sepharose Fast Flow chromatography (all Pharmacia). There was no cross-contamination between HMWK and LMWK as confirmed by immunoblotting of the preparations after SDS-PAGE. Assays were performed with