Fructosyltransferase levan

Two extracellular D-fructans, (2- 6)-linked S-D-fructofuranan or levan and the less common corresponding (2 l)-linked polysaccharide, of the inulin type, are elaborated by different bacteria. These polysaccharides are formed from sucrose by the action of sucrose fructosyltransferases. Terminal )S-D-fructofuranosyl groups are present in some bacterial heteropolysacchar-... 

S. A. van Hijum, K. Bonting, M. J. van der Maarel, and L. Dijkhuizen, Purification of a novel fructosyltransferase from Lactobacillus reuteri strain 121 and characterization of the levan produced, FEMS Microbiol. Lett., 205 (2001) 323-328. 

Dijkhuizen and coworkers identified and characterized a Lactobacillus levansucrase (systematic name sucrose [6)-P-D-fructofuranosyl-(2 ]n a-D-glucopyranoside 6-P-D-fructosyltransferase EC 2.4.1.10) from L. reuteri strain 121, which could produce a high molecular weight levan polysaccharide from fructose [207]. 

Fig. 13 Inulin and levan formation by fructosyltransferase from sucrose...

Levan has a backbone of p-(2 6) linked o-fructose and occurs as high molecular weight polysaccharide in microorganisms. It is accessible from sucrose by use of the enzyme levansucrase (sucrose 6-fructosyltransferase (FTF, EC 2.4.1.10)). Either culture broth of bacterial strains like Bacillus or Zymomonas or the cell-free supernatant can be used for the enzymatic reaction with sucrose. The molecular weight and the viscosity of levan depend on the strain used and the reaction conditions [131, 134]. Even though levan has interesting properties, it has never gained extensive industrial use up to now [134]. 

Stereoselective chemical synthesis of DFAs is instrumental in obtaining pure standards for the validation of analytical methods for the identification and quantification of DFAs in mixtures, particularly in food products. Yet it is inadequate for mass production of DFAs or nutritional applications. Biotechnological approaches using inulin or levan fructosyltransferases, while limited to certain diastereomers, show much promise in these respects. Most of the reports on enzymatic synthesis of DFAs are related to the monospiranic difuranose DFA 111 (1) and the non-spiranic DFA rV (15), while reports on the dispiranic DFA I (10) are much less frequent. Their synthesis has become an issue of industrial interest [56]. 

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