FATE OF 2 MAST-CELL TRYPTASES IN V3 MASTOCYTOSIS AND NORMAL BALB C MICE UNDERGOING PASSIVE SYSTEMIC-ANAPHYLAXIS - PROLONGED RETENTION OF EXOCYTOSED MMCP-6 IN CONNECTIVE TISSUES, AND RAPID ACCUMULATION OF ENZYMATICALLY ACTIVE MMCP-7 IN THE BLOOD/

The mouse mast cell protease granule tryptases designated mMCP-6 and m MCP-7 are encoded by highly homologous genes that reside on chromosome 17. Because these proteases are released when mast cells are activate d, we sought a basis for distinctive functions by examining their fate s in mice undergoing passive systemic anaphylaxis. 10 min-1 h after an tigen (Ag) was administered to immunoglobulin (Ig)E-sensitized mice, n umerous protease/proteoglycan macromolecular complexes appeared in the extracellular matrix adjacent to most tongue and heart mast cells of normal BALB/c mice and most spleen and liver mast cells of V3 mastocyt osis mice. These complexes could be intensively stained by anti-mMCP-6 Ig but not by anti-mMCP-7 Ig. Shortly after Ag challenge of V3 mastoc ytosis mice, large amounts of properly folded, enzymatically active mM CP-7 were detected in the plasma. This plasma-localized tryptase was s imilar to 150 kD in its multimeric state and similar to 32 kD in its m onomeric state, possessed an NH2 terminus identical to that of mature mMCP-7, and was not covalently bound to any protease inhibitor. Compar ative protein modeling and electrostatic calculations disclosed that m MCP-6 contains a prominent Lys/Arg-rich domain on its surface, distant from the active site. The absence of this domain in mMCP-7 provides a n explanation for its selective dissociation from the exocytosed macro molecular complex. The retention of exocytosed mMCP-6 in the extracell ular matrix around activated tissue mast cells suggests a local action . In contrast, the rapid dissipation of mMCP-7 from granule cores and its inability to be inactivated by circulating protease inhibitors sug gests that this tryptase cleaves proteins located at more distal sites .