Intermolecular fructosyl and levanbiosyl transfers by levan fructotransferase of Arthrobacter ureafaciens

A purified levan fructotransferase preparation from the culture of the bacterium Arthrobacter ureafaciens, which produces di-D-fructose 2,6':6,2' dianhydride (difructose anhydride IV) from levan by an intramolecular levan fructosyl transfer (ILFT) reaction, was found to produce a trioligofructan and a tetraoligofructan from levan in the presence of levanbiose, indicating the intermolecular fructosyl and levanbiosyl transfer (LFT and LBT) reactions. The tri- and tetraoligofructans were identified to be levantriose and -tetraose respectively. Increase in the levanbiose concentration brought about increased production of both oligofructans with decreased formation of difructose anhydride IV, supporting the previous theory proposed by Tanaka et al. (1983) that the ILFT, LFT, and LBT reactions are catalyzed by the same enzyme. In addition, there existed a roughly stoichiometric relationship between the increase and decrease in the productions of these oligofructans, and the LBT reaction was found to occur more intensively than the LFT reaction. Acceptor specificity of the LFT and LBT reactions was studied using fifteen sugars including mono-, di-, and trisaccharides. The enzyme showed both of the reactions only with levanbiose, -triose, and kestose, indicating that the exposed non-reducing levanbiosyl residue was essential for the acceptor and suggesting the existence of a levanbiosyl acceptor site on the enzyme molecule.