Galactoglucomannans

Following previous attempts to isolate a pure mannan from wood, Hess and Liidtke reported the isolation of such a polymer from a spruce sulfite pulp. Husemann, much later, obtained a similar product from a spruce holocellulose. It is now clear that these polysaccharides could not possibly have been mannans. Wise and Ratliff found that over half of the D-mannose residues in black spruce wood are intimately associated with the a-cellulose portion, perhaps as an integral part of the cellulose. A skinlike substance, insoluble in cuprammonia, was isolated by Rollin- 

It was pointed out that direct attachment of the D-galactose residues to the hexosan framework is only one possibility. It was observed that the D-galactosidic linkage is quite labile to acids. Polysaccharides of similar composition were isolated from western hemlock and redwood Sequoia sempervirens), and it was suggested that water-soluble galactoglucomannans may be of general occurrence in softwoods. 

Somewhat later, a general method for isolating galactoglucomannans 

Obviously, Meier s results may equally well be interpreted in terms of a triheteropolymer galactoglucomannan. Glucomannans are well known for their insolubility in water and their limited solubility in certain aqueous alkalis, whereas galactomannans are water-soluble. A glucomannan and a galactomannan, if really present, should be separable. It also appears 

In addition to the galactoglucomannans discussed here, many softwoods yield, on direct extraction with water, small proportions of a very similar galactoglucomannan, often in admixture with an arabinogalactan, as mentioned previously (see pp. 426 and 427). ° This polysaccharide is probably extracellular, and will be treated separately. 

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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...

CeU waUs of woods contain other subgroups of hemiceUuloses, in particular those composed primarily of D-mannopyranosyl or D-galactopyranosyl units. Glucomannans [11078-31-2] comprise 3—5% of the wood of angiosperms and 3—12% of the wood of gymnosperms. Galactoglucomannans [9040-29-3] are also common. 

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

Shimizu, K., Teratini, F., Hashi, M. and Miyazaki, K. (1972). Effect of the thermal treatment on wood hemicelluloses. VI. Studies on the thermal analysis of arabinogalactan, and O-acetyl and deacetylated-galactoglucomannans. Mokuzai Gakkaishi, 18(2), 79-84. 

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.

Cartier, N., Chambat, G., Josleau, J. -P. (1988). Cell wall and extracellular galactoglucomannans from suspension-cultured Rubus fmcticosus cells. Phytochemistry, 27, 1361-1364. 

Eda, S., Akiyama, Y, Kato, K., Ishizu, A., Nakano, J. (1985). A galactoglucomannan from cell walls of suspension-cultured tobacco Nicotiana tabacum) cells. Carbohydr. Res., 137, 173-181. 

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. 

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