LOCALIZATION AND CHARACTERIZATION OF ALPHA-GLUCOSIDASE ACTIVITY IN LACTOBACILLUS-BREVIS

Lactobacillus brevis is found together with the yeast Brettanomyces lambicus during the overattenuation process in spontaneously fermented iambic beer. An isolated L. brevis strain has been shown to produce an alpha-glucosidase with many similarities to the glucosidase earlier found in B. lambicus. The enzyme was purified by ammonium sulfate precipitation, gel (Sephadex G-150 and Ultrogel AcA-44) filtration, and ion-exchange chromatography (DEAE-Sephadex A-50). The molecular weights of the enzyme, as determined by gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were about 50,000 and 60,000, respectively. Optimum catalytic activity was obtained at 40 degrees C and pH 6.0. The enzyme showed a decrease of hydrolysis with an increase in the degree of polymerization of the substrate. The K-m values for p-nitrophenyl-alpha-D-glucopyranoside, maltose, and maltotriose were 0.51, 3.0, and 5.2 mM, respectively. There was lack of inhibition by 0.15 mM acarbose and 0.5 M turanose, but the enzyme was inhibited by Tris (K-i value of 25 mM). The alpha-glucosidase of L. brevis together with the enzyme of B. lambicus seems to be a key factor in the overattenuation of iambic beer, although the involvement of other lactic acid bacteria (pediococci) cannot be excluded.