Polysaccharide chains structures

X-Ray diffraction analysis of oriented polysaccharide fibers has had a long history. Marchessault and Sarko discussed this topic in Volume 22 of Advances, and a series of articles by Sundararajan and Marchessault in Volumes 33, 35, 36, and 40 surveyed ongoing developments. The comprehensive account presented here by Chandrasekaran (West Lafayette, Indiana) deals with some 50 polysaccharides, constituting a wide range of structural types, where accurate data and reliable interpretations are available. The regular helical structures of the polysaccharide chains, and associated cations and ordered water molecules, are presented in each instance as stereo drawings and discussed in relation to observed functional properties of the polymers. 

Figure 13-13. The glycogen molecule. A General structure. B Enlargement of structure at a branch point. The molecule is a sphere approximately 21 nm in diameter that can be visualized in electron micrographs. It has a molecular mass of 10 Da and consists of polysaccharide chains each containing about 13 glucose residues. The chains are either branched or unbranched and are arranged in 12 concentric layers (only four are shown in the figure). The branched chains (each has two branches) are found in the inner layers and the unbranched chains in the outer layer. (G, glycogenin, the primer molecule for glycogen synthesis.)...

A regular fine structure causing maximal hydrogen bonding between the molecules reduces the possibility of reversible processes and therefore reduces the gel-forming properties of the compound. Other polysaccharides with different types of monomers or with branched chain structures can be treated in a similar manner. However, much more study of their fine structure and the accessibility of their functional groups is necessary. 

Yeast Insoluble Polysaccharide. The structure of an insoluble polysaccharide from the yeast Saccharomyces cerevisiae was investigated by Zechmeister and Toth,90a and also by Hassid, Joslyn and McCready.904 The isolation904 of 2,4,6-trimethyl-D-glucose as the sole product of the hydrolysis of the methylated polysaccharide indicated a chain of gluco-pyranose units joined by 1,3-glucosidic linkages. 

A bacterial phosphatidylinositol specific phospholipase C (PI-PLC) had been available for many years before it was demonstrated to strip a number of membrane-bound proteins from eukaryotic cell surfaces [1], Such proteins are anchored by a PI moiety in which the 6 position of inositol is glycosidically linked to glucosamine, which in turn is bonded to a polymannan backbone (Fig. 3-10). The polysaccharide chain is joined to the carboxyl terminal of the anchored protein via amide linkage to ethanolamine phosphate. The presence of a free NH2 group in the glucosamine residue makes the structure labile to nitrous acid. Bacterial PI-PLC hydrolyzes the bond between DAG and phosphati-dylinositols, releasing the water-soluble protein polysac charide-inositol phosphate moiety. These proteins are tethered by glycosylphosphatidylinositol (GPI) anchors. 

The structure of the leaving group is a decisive factor for donor properties. Natural substrates for glycosidases are polysaccharidic chains and the corresponding disaccharides are still used in transglycosylation reactions as... 

Following with bacterial infections and anti-adhesion strategies,86 88 NMR based structural studies have been conducted on O-polysaccharide chains in these past few years,38 40,42,43 in order to elucidate the molecular basis and the role of the lipopolysaccharides in these pathologies. 

We generally describe the structure of both synthetic and natural polymers in terms of four levels of structure primary, secondary, tertiary, and quaternary. The primary structure describes the precise sequence of the individual atoms that compose the polymer chain. For polymers that have only an average structure, such as proteins, polysaccharides, and nucleic acids, a representative chain structure is often given. 

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