Changes of dipeptidyl aminopeptidase activities in mouse skeletal muscle following prolonged running

1. Activities of dipeptidyl aminopeptidases (DAP), leucine arylamidase and beta-glucuronidase were assayed in red and white parts of mouse quandriceps femoris muscle 3 and 7 days after a single bout of prolonged running. 2. The activities of lysosomal acid hydrolases (DAP I, DAP II and beta-glucuronidase) were highly increased on the 3rd day after the exertion and then decreased by the 7th day. The response was more prominent in red than in white skeletal muscle. 3. The activities of two microsomal hydrolases, DAP IV and leucine arylamidase, increased much less than those of the lysosomal acid hydrolases. The highest activities were recorded on the 7th day after exertion. 4. The activity of DAP III, a cytoplasmic peptidase, was unaffected in red muscle but slightly increased in white muscle. 5. The protein content of red skeletal muscle, but not that of white muscle, decreased transiently after the running. 6. It seems that strenuous exercise selectively stimulates the lysosomal proteolytic system in skeletal muscle, while the others are less affected.