Elevated temperature and chemical modification selectively abolishes levanforming activity of levansucrase of Zymomonas mobilis

A levansucrase (SacB) of Zymomonas mobilis was purified to electrophoretic homogeneity from a recombinant Escherichia coli. The 55 kDa enzyme hydrolys ed beta-fructosides but not alpha-glucosides and catalysed levan formation from sucrose as well as raffinose. The optimum temperature for polymerase a ctivity (30 degrees C) was lower than that for hyrolase activity (50 degree s C). In contrast to other levansucrases, polymerase activity of levansucra se was inhibited by para-chloromercuribenzoate (1 mM) but with little or no effect on hydrolase activity. Selective modulation of polymerase activity by this inhibitor will be useful in revealing the mechanism of levansucrase catalysis.