A major serine protease in rat skeletal muscle: evidence for its mast cell origin

The physical, chemical, and immunologic properties of a protease from rat skeletal muscle, proposed to function in the degradation of certain intracellular enzymes, are identical to those of a chymotrypsin-like serine protease isolated from peritoneal mast cells. The results of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and 8 M urea indicate that the two rat proteases have identical mobilities corresponding to a molecular weight of 26,000. The relative amino acid compositions of the proteases are nearly identical. Immunodiffusion tests for crossreaction between the muscle protease and antisera directed toward mast cell protease indicate that the former is immunologically identical to mast cell protease. The first 35 amino-terminal residues of the two enzymes are identical and indicate homology of these proteins to other mammalian serine proteases. The sequence analysis of the protease from muscle was extended for an additional 16 positions, and comparison of this amino-terminal sequence with that of a similar enzyme from small intestine showed approximately 75% sequence identity. In contrast, only 40% of the residues in this region of bovine chymotrypsin A were found at corresponding loci in rat muscle protease. It is concluded that the protease from muscle or mast cells is closely related to the enzyme from small intestine which recently was localized in the "atypical" mast cells of gut mucosa [Woodbury, R. G., Gruzenski, G. M. & Lagunoff, D. (1978) Proc. Natl. Acad. Sci. USA 75, 2785-2789].