Purification and characterization of intracellular and extracellular α-glucosidases from Geobacillus toebii strain E134.

Two different α-glucosidase-producing thermophilic E134 strains were isolated from a hot spring in Kozakli, Turkey. Based on the phenotypic, phylogenetic and chemotaxonomic evidence, the strain was proposed to be a species of G. toebii. Its thermostable exo-α-1,4-glucosidases also were characterized and compared, which were purified from the intracellular and extracellular fractions with estimated molecular weights of 65 and 45 kDa. The intracellular and extracellular α-glucosidases showed optimal activity at 65 °C, pH 7.0, and at 70 °C, pH 6.8, with 3.65 and 0.83 K(m) values for the pNPG substrate, respectively. Both enzymes remained active over temperature and pH ranges of 35-70 °C and 4.5-11.0. They retained 82 and 84% of their activities when incubated at 60 °C for 5 h. Their relative activities were 45-75% and 45-60% at pH 4.5 and 11.0 values for 15 h at 35 °C. They could hydrolyse the α-1,3 and α-1,4 bonds on substrates in addition to a high transglycosylation activity, although the intracellular enzyme had more affinity to the substrates both in hydrolysis and transglycosylation reactions. Furthermore, although sodium dodecyl sulfate behaved as an activator for both of them at 60 °C, urea and ethanol only increased the activity of the extracellular α-glucosidase. By this study, G. toebii E134 strain was introduced, which might have a potential in biotechnological processes when the conformational stability of its enzymes to heat, pH and denaturants were considered.