Characterization of an Exo‐β‐d‐Fructosidase from Streptococcus mutans Ingbritt

An extracellular enzyme β‐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 β‐(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.