Mechanism of Synthesis of Levan by Bacillus natto Levansucrase (糖質関連酵素化学シンポジウム) Mechanism of Synthesis of Levan by Bacillus natto Levansucrase
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Levansucrase acts on sucrose usually to synthesize a fructan which contains a sucrose unit at one terminus of the molecule and has branches formed by β-2, 1-fructofuranosyl linkage. The transfer of fructosyl residue to an acceptor by the enzyme is carried out from not only sucrose but also oli gosaccharides which contain a sucrose unit such as raffinose or fructosyl maltoside, fructosyl cellobioside, fructosyl lactoside, etc., which can be synthesized from sucrose in the presence of an acceptor sugar (maltose, cellobiose, lactose, etc.) by levansucrase. Soybean contains such oligosaccharides other than sucrose. We isolated levan from fermented soybean (Natto) and analyzed the molecular weight and terminus of the molecule. It was revealed that the molecular weight was about 1.1 × 10<SUP>4</SUP> by HPLC using molecular markers of pullulans, and the levan isolated contained a stachyose unit at the terminal of the molecule. It was thought that the enzyme might have a donor binding site (with a high affinity toward sucrose) and an acceptor binding site in the molecule. Because synthesized trisaccharide contained only raffinose and the terminal unit of levan was raffinose in the case of levan synthesized from sucrose in the presence of melibiose, although the levan synthesized from sucrose alone contained kestose (mainly the 1-kestose and 6-kestose, ca .1:1) as the terminal unit of the levan.
- Journal of Applied Glycoscience
Journal of Applied Glycoscience 49(2), 229-237, 2002-04-01
The Japanese Society of Applied Glycoscience