2.5. Measurement of enzyme activities
The enzyme extract for cathepsin assays was prepared from 2.5 g
of muscle homogenised in 25 mL of 50 mM sodium citrate buffer, pH
5.0, containing 1 mM EDTA and 2% (v/v) Triton X-100, whereas 4.0 g
of muscle was employed for peptidases (aminopeptidases and
dipeptidylpeptidases) assays in 20 mL of 50 mM phosphate buffer,
containing 5 mM EGTA, pH 7.5. In all cases, the extracts were
homogenised using a Polytron homogeniser (Kinematica GmbH,
Luzerne, Switzerland) 3 × 10 s at 27.000 rpm in an ice bath and then
centrifuged at 10,000 ×g for 20 min at 4 °C. The resulting supernatants
were each filtered through glass wool and used for further enzymatic
assays.