The Molecular Structure of Low and High Molecular Weight Levans Synthesized by Levansucrase

The levan synthesized by Bacillus subtilis levansucrase in the presence of alcohols was of only high molecular weight, while in solutions of high ionic strength only low molecular weight (MW) levan was produced. The addition of low MW levan to the enzyme reaction mixture at low ionic strength stimulated synthesis of a high MW levan, but the levan added was not incorporated into this high MW levan. Methylation analysis revealed that low MW levans contained glucose, which was isolated as 2,3,4,6-tetra-O-methyl alditol acetate, showing that the glucose units existed as terminal residues. The molecular weight of levan estimated on the basis of glucose content coincided with that determined by the gel filtration method. Methylation analysis also revealed that the number of fructose residues of the linear fraction linked by →6(F)2→ type bonds was 22 for levan with a molecular weight of (8.4–22)×10³, while it was 11 for that of 2, 000×10³. The number of $(F)→1→62→$(F)2→ type branched residues increased with increase in the molecular weight of the levan synthesized.