Purification and characterization of thermostable α-amylase from germinating sword bean (Canavalia gladiata (jacq.) DC.) seeds

Abstract

The thermostable α-amylase from germinating sword bean (Canavalia gladiata (Jacq.) DC.) seeds (CgAmy) was successfully purified by a combination of ammonium sulphate fractionation and Epoxy-activated Sepharose 6B affinity chromatography. The purified α-amylase showed 507.8 fold with a specific activity of 750.0 U/mg. SDS-PAGE of the purified enzyme revealed a single protein band of 50.0 kDa. Purified enzyme was confirmed as α-amylase type by LC-MS/MS analysis and activity on specific substrate of ethylidene-pNP-G7. The CgAmy revealed extreme activity at a high temperature of 50.0–70.0°C with optimum activity at 70.0°C. The optimal pH of enzyme activity was observed at 6.0. The CgAmy exhibited stability in pH range of 5.0–8.0 and highly thermostable with a temperature of 40.0–60.0°C. The kinetic parameters Km for hydrolysis of starch were found to be 3.12 mg/ml. The α-amylase activity was enhanced in the presence of Co2+ and β-mercaptoethanol. While, Na2+, K2+, Ca2+, Mg2+, Zn2+, Ba2+, Fe2+ and Cd2+ slightly inhibited α-amylase activity. Interestingly, the CgAmy displayed stability towards some organic solvents and detergents. Stability at high temperature and some metal ions, organic solvents and detergents indicated that this enzyme has potential for various applications.