Serine protease that selectively cleaves Arg-|-Xaa bonds. Inhibited by the serine protease inhibitors, antipain, aprotinin, DFP, leupeptin, STI and TLCK, and by the cysteine proteinase inhibitors DTNB and to a lesser extent E-64. Not inhibited by the metalloproteinase inhibitor EDTA. Optimum pH is 8.0. Active from pH 5.0 to at least 9.0. Optimum temperature is 55 degrees Celsius. Detected in muscle (at protein level). Belongs to the peptidase S1 family.