Structural characterization of the maltose acceptor-products synthesized by Leuconostoc mesenteroides NRRL B-1299 dextransucrase

The glucooligosaccharides (GOS), produced by Leuconostoc mesenteroides NRRL B-1299 dextransucrase through an acceptor reaction with maltose and sucrose, were purified by reverse phase chromatography. Logarithmic plots of retention time vs. dp of the GOS gave three parallel lines suggesting the existence of at least three families of homologous molecules. The structure (13C and 1H NMR spectroscopy) and reactivity of the purified molecules of the three families were investigated. All the products bear a maltose residue at the reducing end. The GOS in the first family (named OD) contained additional glucosyl residues all alpha-(1-->6) linked. The smallest molecule in this first series was panose or alpha-D-glucopyranosyl-(1-->6)-D-maltose (dp 3). All the OD molecules were shown to be good acceptors for dextransucrase in the presence of sucrose. The second family, named R, was composed of linear GOS containing alpha-(1-->6)-linked glucosyl residues and a terminal alpha-(1-->2)-linked residue at the non-reducing end of the molecule; the smallest molecule in this family was alpha-D-glucopyranosyl-(1-->2)-D-panose (dp 4). The third family, R', was formed of GOS containing additional residues linked through alpha-(1-->6) linkages that constitute the linear chain, and an alpha-(1-->2)-branched residue located on the penultimate element of the chain, near the non-reducing end. The smallest molecule in this series is alpha-D-glucopyranosyl-(1-->6)-alpha-D-glucopyranosyl-(1-->2)]-alpha-D- glucopyranosyl-(1-->6)-D-panose, dp 6. R and R' GOS are very poor acceptors for L. mesenteroides NRRL B-1299 dextransucrase. This study makes it possible to suggest a rather simple reaction scheme, where molecules Ri, R'i and ODi of the same dp all result from the glucosylation of the same GOS: ODi-l.