New source of the thermostable α-glucosidase suitable for single step starch processing

Abstract

Thermus thermophilus contains α-glucosidase that is located in the cell cytoplasm. The highest enzyme activity was achieved after 25–30 h of microorganism cultivation at 70 °C in a medium containing 0.8% peptone, 0.4% yeast extract and 0.2% Na Cl. Addition of 2% of starch, maltose or glucose to the medium enhanced the enzyme activity by 83, 72 and 31%, respectively. The enzyme was purified 7.2-fold by combination of ammonium sulphate precipitation and ion-exchange chromatography on Sepharose CL-6B. The enzyme preparations exhibited highest specific activity for pNPG hydrolysis (1.94 U mg −1) at pH 6.2 and 85 °C. The activity of partially purified enzyme was almost unchanged during 5 h of incubation at 75 °C in phosphate-citrate buffer (pH 6.2) and the half-life of this enzyme incubated at 85 °C was 2 h. Rate of pNPG cleavage catalysed by the α-glucosidase was 9.5-times higher than that in the case of maltose hydrolysis. Furthermore, this enzyme shows remarkable activity toward maltose and maltotriose. With maltotetraose, maltopentaose and maltohexaose the reaction rate decreased with increase in molecular weight of the substrate.