Preclinical increase in activity of muscle microsomal trypsin-like protease in murine muscular dystrophy, C57BL/10-mdx

Preclinical alterations of protease activities in skeletal muscles from 10-day-old dystrophic mouse, C57BL/10-mdx, were examined by using 10 fluorogenic peptide substrates. Among the activities tested, only Boc-Val-Pro-Arg-MCA-hydrolyzing enzyme of the muscle microsomes showed an about 6-fold higher level of activity in mdx mouse. The increase in activity was not observed in tissues other than skeletal muscle. The enzyme had a pH optimum between 8.5 and 11.0, and was inhibited with DFP and variety of trypsin inhibitors. The enzymatic activity transiently increased at 1-2 weeks of age, the preclinical or very early stage of the disease. These results imply that the increased level of a trypsin-like protease possibly present in muscle microsomes may be closely related to the manifestation of muscular dystrophy.