Neutral saccharides

To characterize modifications in the cell wall composition of transgenic invertase plants we determined the distribution of neutral saccharides (Fig. 1). Obviously, the relative amounts of fucose and mannose were slightly reduced in leaf 6 of transgenic plants, whereas arabinose was increased. The other saccharides remained unchanged. 

Ion chromatography has become available and is used for sugar analysis. In this system a high-performance anion exchange column is used at high pH. This separation works because neutral saccharides behave as weak acids. Table 1 shows some pKa values. 

Que, A. H., and Novotny, M. V. (2002). Separation of neutral saccharide mixtures with capillary electrochromatography using hydrophilic monolithic columns. Anal. Chem. 74, 5184-5191. 

Fraser JRE. Foo WK. Maritz JS. Viscous interactions of hyaluronic acid with some proteins and neutral saccharides.. AnnRheutn. Dis. 1972 31 513-20. 

The fact that the neutral saccharide residue is trapped on the column and subsequently can be eluted as though it contains carboxylate functionality frirther supports the thesis that the saccharide monomer is incorporated into the poly(acrylic acid). In a control experiment, glucose was not retained on the ion exchange column in the presence of the copolymer while the copolymer was. These observations were used to advantage in the determination of saccharide monomer incorporation into the acrylic acid copolymer. A solution of polymer made from a feed containing 2 mole% monomer 5f that was not otherwise purified was subjected to the solid phase extraction technique. Forty-six percent of the saccharide present in the copolymer solution prior to solid phase extraction was not retained on the solid phase extraction medium 54% of the saccharide was retained and therefore bound to the copolymer. This indicates that a feed of 2 mole% of this saccharide monomer leads to the incorporation of 1.1 mole% monomer in the copolymer. Similar levels of monomer incorporation were observed in other copolymerizations of monomer 5f and with monomer 5e (75). 

Mono- and di saccharides are colourless solids or sjrrupy liquids, which are freely soluble in water, practically insoluble in ether and other organic solvents, and neutral in reaction. Polysaccharides possess similar properties, but are generally insoluble in water because of their high molecular weights. Both poly- and di-saccharides are converted into monosaccharides upon hydrolysis. 

The FTIR spectra of citrus pectin and wheat straw XRPP (Figure 1) appeared to be similar. Both of the spectra have absorptions at 1740, 1608, 1430, 1360, 1244, 1080, 1060, 1035, 890 and 524 cm. The pectic substances belong to a class of carboxy poly saccharides which differ from neutral polysaccharides, with an intense band in the region 1740 cm l (for salts 1608 cm ) related to vibrations of the carboxyl group... 

Figure 1, Relative distribution of neutral cell wall saccharides. The bar indicates the means +/-S.E. of 6 independent measurements.

It is necessary to remember that as well as organic cross-links, elements such as boron, silicon and calcium cross-link all the major external proteins and saccharides even in the walls of prokaryotes. Many of the cross-linking binding sites are of oxidised side chains of biopolymers. As described in Section 8.10, certain of these elements form mineral deposits but now these minerals are frequently found inside the multi-cellular organisms. Here, we see a great difference between the chemo-types of plants and animals. The acidity of the extracellular fluids of plants differs from the neutral fluid of animals. It is not possible to precipitate calcium carbonates (shells) or phosphates (bones) in plants due to the weak acid character of these anions (see Table 8.12). Plants therefore precipitate silica and calcium... 

The D-galactosyl residues are the same as in disaccharide 33, and the fact that ribitol is substituted at 0-2 was evident from the methyl-ation analysis. Finally, a nonreducing tetrasaccharide was obtained, containing D-galactose, 2-acetamido-2-deoxy-D-galactose, and ribitol residues in the proportions 2 1 1. From these results, and periodate-oxidation studies, structure 36 was proposed for the neutral hexa-saccharide. 

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