Characterization of an exo-beta-D-fructosidase from Streptococcus mutans Ingbritt

An extracellular enzyme beta-D-fructosidase was purified from the culture supernatant of Streptococcus mutans Ingbritt and characterized. The molecular weight of the enzyme was 127,000 as determined by SDS-polyacrylamide gel electrophoresis. The enzyme was specific for levan which mainly consists of beta-(2,6)-linked D-fructose and was also able to hydrolyze inulin, sucrose and raffinose at the activities of 13, 9 and 5% of that hydrolyzing levan, respectively. The pH optima for levan, inulin and sucrose were approximately 5.5, 6.0 and 5.0, respectively. The enzyme was optimally reactive at 55 C for levan. The enzyme was inhibited by Fe3+, Hg2+ and Zn2+ and not by either anionic or non-ionic detergents. Paper chromatographic analysis revealed that the enzyme attacked levan by an exo-type mechanism.