Thermal stability of α-amylase in aqueous cosolvent systems.

ABSTRACT

The activity and thermal stability of α-amylase were studied in the presence of different concentrations of trehalose, sorbitol, sucrose and glycerol. The optimum temperature of the enzyme was found to be 50 ± 2°C. Further increase in temperature resulted in irreversible thermal inactivation of the enzyme. In the presence of cosolvents, the rate of thermal inactivation was found to be signifi cantly reduced. The apparent thermal denaturation temperature (T m ) app and activation energy (E a ) of α-amylase were found to be signifi cantly increased in the presence of cosolvents in a concentration-dependent manner. In the presence of 40% trehalose, sorbitol, sucrose and glycerol, increments in the (T m ) app were 20°C, 14°C, 13°C and 9°C, respectively. The E a of thermal denaturation of α-amylase in the presence of 20% (w/v) trehalose, sorbitol, sucrose and glycerol was found to be 126, 95, 90 and 43 kcal/mol compared with a control value of 40 kcal/mol. Intrinsic and 8-anilinonaphathalene-1-sulphonic acid (ANS) fl uorescence studies indicated that thermal denaturation of the enzyme was accompanied by exposure of the hydrophobic cluster on the protein surface. Preferential interaction parameters indicated extensive hydration of the enzyme in the presence of cosolvents.