Galactoglucomannans structure

Fig. 9. Partial structural formulas and shorthand notations for principal hemiceUuloses found in wood, where the sugar units ate noted as P-D-xylopyranose (Xylp), 4-Omethyl-a-D-glucopyranosyluronic acid (GlupU), a-L-arabinofuranose (Araf), P-D-glucopyranose (Glup), P-D-mannopyranose (Manp), and P-D-galactopyranose (Galp) for (a) arabino-4-O-methylglucuronoxylan from softwood, (b) 0-acetyl-galactoglucomannan from softwood, and...

Figure 3.4 Structures of the galactoglucomannan (a heteromannan) known to occur in the primary cell walls of several species of eudicotyledons and the glucuronoarabinoxylan (a heteroxylan) known to occur in the primary cell walls of sycamore (Acer pseudoplatanus). The structures of the heteromannans and heteroxylans in potato cell walls are unknown.

Sims, I. M., Craik, D. J., Bacic, A. (1997). Structural characterization of galactoglucomannan secreted by suspension-cultured cells of Nicotiana plumbaginifolia. Carbohydr. Res., 303, 79-92. 

In describing and interpreting some of the more important properties of plant galactomannans, comparisons will be made with structurally similar polysaccharides, including the closely related glucomannans and galactoglucomannans, and those based on (1 — 4)-/3-D-xylan main-chains (for example, the arabinoxylans) and (1 — 4)-/3-D-glucan main-chains [for example, the amyloids and sodium 0-(carboxymethyl)cellulose]. 

Similar structural problems exist for the distribution of side chains in galactoglucomannans, xyloglucans, arabinoxylans, and 4-0-methylglucuronoxylans, and even for the distribution of acetyl groups in glucomannans and for related features in many other polysaccharides. 

Fig. 3-12. The structure of galactoglucomannans. Sugar units 1, /3-D-glucopyranose (Glcp) 2, /3-D-mannopyranose (Manp) 3, /3-D-galactopyranose (Galp). R = CH3CO or H. Below the abbreviated formula showing the proportions of the units (galactose-rich fraction).

On extraction of wood of white spruce with water, Adams obtained two polysaccharides, one of which, a galactoglucomannan, will be discussed later (see p. 458). The other, an acidic arabinogalactan still containing some xylan, was subjected to a structural investigation. The methylation data (see Table XI) were very similar to those observed for the polysaccharide... 

Kg. 24. Partial chemical structure of some hemicelluloses A — 0-acetyl-(4-0-methyl-glucurono)xylan from hardwood B = arabino-(4-0-methylglucurono)xylan from softwood C = 0-acetyl-galactoglucomannan D = arabinogalactan from larch wood (138). 

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