SHEEP MAST-CELL PROTEINASE-1, A SERINE PROTEINASE WITH BOTH TRYPTASE-LIKE AND CHYMASE-LIKE PROPERTIES, IS INHIBITED BY PLASMA PROTEINASE-INHIBITORS AND IS MITOGENIC FOR BOVINE PULMONARY-ARTERY FIBROBLASTS

Sheep mast cell proteinase-1 (sMCP-1), a serine proteinase with dual c hymase/tryptase activity, is expressed in gastrointestinal mast cells, and released systemically and on to the mucosal surface during gastro intestinal nematode infection. The potential for native plasma protein ase inhibitors to control sMCP-1 activity was investigated. Sheep alph a(1)-proteinase inhibitor (alpha(2)PI) inhibited sMCP-1 slowly, with s econd-order association rate constant (k(ass)) 1.1 x 10(3) M-1.s(-1), whereas sheep contrapsin inhibited trypsin (k(ass) 2.2 x 10(6) M-1.s(- 1)) but not sMCP-1. Western-blot analysis and gel filtration showed th at when added to serum or plasma, sMCP-1 was partitioned between alpha (1)PI and alpha(2)-macroglobulin. The possibility that significant cle avage of plasma proteins could occur before sMCP-1 was inhibited was i nvestigated using gel filtration and SDS/PAGE after adding sMCP-1 to p lasma. Cleavage of ovine fibrinogen occurred in the presence of excess alpha(1)PI and alpha(2)-macroglobulin, the alpha-chain being cleaved C-terminally and the beta-chain at the putative Lys-27. In addition, s MCP-1 was found to be mitogenic for bovine pulmonary artery fibroblast s, but was not mitogenic in the presence of soya-bean trypsin inhibito r. In terms of fibrinogen cleavage and fibroblast stimulation, sMCP-1 shows functional similarities to mast cell tryptase.