2. Synthesis of fructans
Because fructans are synthesized from sucrose by
repeated fructosyl transfer from a fructosyl donor, both
inulins and levans usually, but not always, have a terminal
glucose unit. The enzyme generally considered to be
involved in plant fructan synthesis is sucrose-sucrose
fructosyl transferase (EC 2×4×1×99) which catalyses the
transfer of a fructose molecule from one sucrose molecule
to another, leading to kestose formation (glucosyl-1, 2
fructosyl-1, 2 fructose). Chain elongation is mediated by
either 1F– or 6F fructan–fructan–fructosyl (EC 2×4×1×100)
transferase leading to inulin and levans respectively.