2.6. Assessment of crude keratinase
2.6.1. Substrate specificity study
Keratinolytic protease activity was measured using different
substrates (Casein, Azocasein, Keratin, Skim milk, gelatin, albumin,
BSA and hemoglobin) at concentrations (0e4 mg mL 1). The
MichaeliseMenten constant (Km) and the maximum velocity (Vmax)
were calculated by LineweavereBurk plot.
2.6.2. Effect of temperature and pH on activity and stability
The effect of pH on enzyme activity was determined by
measuring protease activity at pH 6e12 using the following buffers:
Na2HPO4eNaH2PO4 (pH 6e8), Tris-HCL (pH 8.5e9.5) and NaOHGlycin
(pH 10e12). Determination of protease activity was done
with the following modifications: the 0.5 mL enzyme sample was
pre-incubated with 0.25 mL of 50 mM above listed buffer solution
for 0e3 days at room temperature. Then 0.25 mL pre-incubated
enzyme solution was added to 0.1 mL azocasein solution and
then incubated according to standard assay condition. The non-pretreated
enzyme which was left at room temperature was considered
as control (100%).
The effect of temperature on crude enzyme was examined at
50e100 C at pH 10. Thermal stability was determined by incubating
enzyme at 50e100 C and pH 10 for 0e180 h. Aliquots were
withdrawn at desired time intervals (20 min) to test the remaining
activity under standard assay conditions. The non-heated enzyme,
which was left at room temperature, was considered as control
(100%).