2.6. Determination of purity and molecular weight of purified amylase
Sodium dodecyl sulphate poly acryl amide gel electrophoresis (SDS–PAGE) was performed to determine and check the molecular weight and purity of purified amylase from pitaya peel.
SDS–PAGE was performed with a gel electrophoresis unit (Bio-Rad) using a 12% acrylamide resolving gel in the presence of 0.1% SDS and a 4.5% stacking gel containing 0.1% SDS according to the method of Laemmli (1970).
The SDS reducing sample buffer and tank buffer were 0.5 M Tris–HCl (pH 6.8) containing 2% SDS and Tris–glycine (0.025 M Tris–HCl, pH 8.3; 0.192 M glycine) with 0.1% SDS, respectively.
A 10% TCA solution was employed to concentrate and precipitate protein samples that had been removed from the top phase.
The precipitation process is important for the removal of salts present in the samples, which if not removed, will affect the electrophoresis process.
Electrophoresis was performed at 110 V and 36 mA for 75 min.
When the run was completed, a solution comprising 0.05% (v/v) Coomassie Brilliant Blue G-250, 30% (v/v) methanol and 10% (v/v) acetic acid, was used to stain the gel.
Protein bands were observed after distaining by employing the same buffer without Coomassie Brilliant Blue.