Age- and activity-related changes in three proteinase enzymes of rat skeletal muscle

The specific activities of three proteinases, cathepsins B, D and H, were measured in two skeletal-muscle types as a function of age (i.e. from large foetal life to old age), and in muscles immobilized at various lengths for 3 days. The activities of the lysosomal endopeptidases B and D, but not H, consistently changed in parallel with previously determined rates of protein breakdown, indicating a good and potentially useful correlation between the two.