Figure 1 Functional assay of calpain‐3 autolytic activity on a muscle biopsy specimen from a normal control. The muscle sample is loaded after conventional treatment for calpain‐3 immunoblot analysis (N) or under experimental conditions that induce spontaneous protein autolysis (incubation in saline solution for different times: 5, 10, 20, and 30 min). The upper panel shows the bands corresponding to the full‐length calpain‐3 protein at 94 kDa molecular weight and the middle panel shows the triplet of calpain‐3 bands at lower molecular weights (60, 58 and 55 kDa) resulting from protein degradation after autolysis. Physiological calpain‐3 autolytic activity leads to almost complete disappearance of the full‐length protein after 5 min and to the production of small‐sized degradation bands after prolonged incubation times. The myosin content in the post‐transfer Coomassie blue‐stained gel (lower panel) is used to normalise the amount of calpain‐3 in each lane.