Effects of the degree of polymerization on the binding of xyloglucans to cellulose.

Xyloglucan oligosaccharides were isolated with various degrees of polymerization (DP) and reduced with tritiated sodium borohydride. The 3H-oligosaccharides were tested for their ability to bind to amorphous and microcrystalline celluloses and to cellulose filter paper. The time course of binding indicated that the radiolabeled oligosaccharides continued to be bound for at least 1 h after heating at 120 degrees C. The binding probably required the organization of the oligosaccharides and celluloses by gradual annealing after heating. Although neither pentasaccharide (glucose: xylose, 3 : 2), heptasaccharide (glucose : xylose, 4 : 3) and nonsaccharide (glucose : xylose : galactose : fucose, 4 : 3 : 1 : 1) failed to bind to the celluloses, binding occurred with oligosaccharides with DP equivalent to more than four consecutive 1,4-beta-glucosyl residues. The extent of binding to the celluloses increased gradually from octasaccharide (glucose : xylose, 5 : 3) to hendecosanosaccharide (glucose/xylose, 12 : 9), with the increase in the DP of 1,4-beta-glucosyl residues. The binding of reduced cello-dextrins to cellulose required at least 4 consecutive 1,4-beta-glucosyl residues. The extent of binding of cellopentitol or cellohexitol to cellulose was similar to that of hendecosanosaccharide, showing lower binding for xyloglucan oligosaccharides in spite of longer chains of 1,4-beta-glucosyl residues. These findings suggest that the mode of binding to cellulose of xyloglucan oligosaccharides is different from that of cello-oligosaccharides.