Serine protease which degrades the myosin heavy chain and tropomyosin, but not actin. Selectively cleaves Arg-|-Xaa bonds. Optimum pH is 9.0. Active from pH 5.0 to 11.0. Optimum temperature is 35 degrees Celsius. Active from 20 to 70 degrees Celsius. Detected in skeletal muscle (at protein level). Belongs to the peptidase S1 family.