α-granule factor V and multimerin degradation.

Western blots compare proteins in QPD (Q) and control (C) platelet lysates (samples with all inhibitors) with the forms generated by incubating normal platelet ionophore releasate (CR; A) or lysate (CL; B, lysate without serine protease inhibitors) with 0, 25, 50, or 100 ng/mL tcu-PA (tcuPA), as indicated. (A) When u-PA was incubated with normal platelet secretory proteins, α-granule factor V was degraded, resulting in a loss of factor V detectable by Western blotting with polyclonal antisera, as in QPD platelets (lanes compare 18 μL lysate and releasate, after reduced 4%-8% SDS-PAGE). (B) Although there was some loss of detectable multimerin in lysates incubated without tcu-PA, tcu-PA reduced the detectable multimerin, as in QPD platelets (lanes compare 15 μL lysates, separated on nonreduced multimer gels and probed with a mixture of monoclonal and polyclonal antimultimerin). Traces of degraded multimerin (bands below the smallest multimerin polymer in normal platelets) were evident in the u-PA digests (B) and in QPD platelets, with longer exposures (not shown).