Enzymatic assay
Characterization of protease
Protease activity was monitored in
triplicate by measuring the increase in cleavage
of short chain polypeptides using the method of
Bezerra et al. (2005) with slight modifications. The
total protease activity was determined using 1%
(w/v) azocasein, prepared in buffers at various pH
levels: 0.1 M glycine–HCl pH 2; 0.1 M citrate
buffer pH 3–5; 0.1 M phosphate buffer pH 6–8;
0.05 M carbonate buffer pH 9–10; 0.05 M
Na2HPO4 buffer pH 11; and 0.1 M KCl - NaOH
buffer pH 12–13. The substrate (500 μl) was
incubated with crude extract (20 μl) and buffer
solution (200 μl) at various pH levels for 60 min
at 30°C. Then, 500 μl of 20% (w/v) trichloroacetic
acid (TCA) was added to stop the reaction. After
15 min, centrifugation was carried out at 10,000 g
for 10 min. The supernatant (1.0 ml) was added to
1 M NaOH (1.5 ml) in a glass cuvette and the
absorbance was measured at 440 nm against a
blank similarly prepared, but without the crude
extract sample. The protease-specific activity was
expressed by the change in absorbance per min
per mg protein of the enzyme extract (ΔAbs min