Purification and preliminary characterization of exo-β-D-fructosidase in Streptococcus salivarius KTA-19

Abstract

Streptococcus salivarius fructosidase (β-D-fructan fructohydrolase, EC 3.2.1.80) was purified to homogeneity. The molecular weight of the fructosidase was estimated to be 83,000 to 85,000 by gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The pH optimum of the enzyme was 7.0, and the isoelectric point was pH 4.7. The purified enzyme preparation hydrolyzed levan, inulin, and several 2-β-linkage-containing oligosaccharides such as sucrose and raffinose, but not melezitose, dextran, and pseudonigeran. The fructosidase was inhibited by Fe3+, Cu2+, Hg2+, and Ag+, but not by Ca2+, Co2+, Mg2+, and Zn2+, at a concentration of 10-3 M. Mn2+ was particularly effective in stimulating activity at the same concentration. The presence of either EDTA or KCN also increased fructosidase activity by 20 to 30%. The enzyme was susceptible to sulfhydryl reagents since p-chloromercuribenzoate (10-7 M) produced 63% inhibition of the activity. However, this inhibition was overcome in the presence of cysteine. This enzyme acts as an exofructosidase since thin-layer chromatographic analysis revealed that D-fructose was formed from levan or inulin by the action of the enzyme.