Application of high-performance liquid chromatography to a study of branching in dextrans

Abstract

The length of the side chains in dextrans has been examined by enzymic hydrolysis and l.c. The linear (IM n ) and branched (B n ) oligosaccharide-products of endodextranase activity were separated by l.c. in water. The branched fractions B 5B 8, obtained from Leuconostoc mesenteroides NRRL B-512(F) dextran were resolved into two components by the same system. Treatment of the isolated components of B 5 with (1→6)-α- d-glucan glucohydrolase, showed that B 5-1, the oligosaccharide eluted in the first peak, was completely hydrolysed to d-glucose and B 4, whereas B 5-2 was not a substrate. The two components of B 6B 8 were all hydrolysed to d-glucose and B 5-2. From a knowledge of the specificity of the two dextranases, together with the results of methylation analysis, it was concluded that the B n -1 series were 3 3-α-isomaltosylisomaltosaccharides, and that the B n -2 series were 3 3-α- d-glucosylisomaltosaccharides. The products are consistent with the structures previously proposed for B 5B 8, and confirm directly that side chains containing two or more glucose residues occur in B-512(F) dextran. The B n -1 series was obtained neither from Streptococcus viridans NRRL B-1351 dextran nor from a chemically synthesized, branched dextran in which the (1→3) branch linkages attached d-glucosyl side-chains exclusively. A determination of B n -2 oligosaccharides and B 4 (3 3-α- d-glucosylisomaltotriose) in the final products indicates the proportion of glucosyl side-chains in dextrans.