Synthesis of novel disaccharides by a newly isolated fructosyl transferase from Bacillus subtilis

Abstract

A new fructosyl transferase (EC 2.4.1.161), with an exceptionally high propensity to form a wide range of α 1–2 linked disaccharides, but which does not form appreciable levan polymer, has been isolated, partially purified, and characterized. It is an extracellular enzyme synthesized in high yield from a newly isolated strain of Bacillus subtilis (NCIB 11871). The enzyme is resistant to proteases and has a very nonspecific aldose (acceptor) binding site. It readily transfers the fructose moiety from α 1−2 linked sugars such as sucrose, raffinose, or stachyose to a wide range of acceptor molecules, including d-xylose, d-galactose, d-mannose, lactose, maltose, d-glucose, l-arabinose, and many substituted sugars. It will also transfer 1,6-dichlorofructose from 1′,6′-dichlorosucrose to glucose. Most significantly, the EC 2.4.1.161 enzyme has a strong tendency to transfer only one fructose moiety, thereby forming sugars one residue longer, i.e., G− F+ X → G+ XF, rather than to form levan polymers by the repetitive transfer of fructose. In the absence of an acceptor, it will transfer fructose to water (i.e., function as an invertase) but at a much slower rate than to a sugar acceptor. In the presence of an acceptor, the rate of sucrose hydrolysis is insignificant. The rate of formation and yield of disaccharide is higher than reported or tested with previously described fructosyl transferases (levansucrases) from other Bacillus or Erwinia organisms. This fructosyl transferase has been used to produce a number of novel disaccharides, such as xylsucrose, galactosucrose, and 6-deoxysucrose.