For the determination of inhibitor sensitivity, the
purified protease solutions (200 ml at 16.5 mg/ml) were
preincubated with 10-fold concentrated stock solutions
of each reagent in the ratio of 1:1 at 30°C for 30 min in
0.02 M borate–NaOH buffer (pH 10) and protease
activity was assayed as described above. PMSF, N-tosyl-L-phenylalaninechloromethyl
ketone (TPCK) and
N-tosyl-L-lysinechloromethyl ketone (TLCK) were prepared
as stock solutions in DMSO. Residual activities
were determined as a percentage of the activity in
control samples without reagent. Appropriate solvent
controls were run in parallel when required. The influence
of different metal ions at 1 and 10 mM final
concentration on protease activities were also determined
using casein as substrate, as described above for
protease inhibitors.