Polysaccharides groups

Many proteins found in nature are glycoproteins because they contain covalently linked oligo- and polysaccharide groups. The list of known glycoproteins includes structural proteins, enzymes, membrane receptors, transport proteins, and immunoglobulins, among others. In most cases, the precise function of the bound carbohydrate moiety is not understood. 

Figure 20.9 Polysaccharide groups on antibody molecules may be oxidized with periodate to create aldehydes. Modification with biotin-hydrazide results in hydrazone linkages. The sites of modification using this technique often are away from the antibody-antigen binding regions, thus preserving antibody activity.

Lipids and proteins that are part of cell membranes often are bonded to small polysaccharide groups that project from the surface of the cell. Slight differences in the structures of polysaccharides that are bonded to lipids in red blood cell membranes of humans are responsible for the A, B, and O blood types. Antibodies recognize these groups and cause cells to clump when their surface groups are not the same as those on the cells of the original individual. 

The other noticeable product of this era was a steady stream of publications, mainly to the Journal of the Chemical Society, but also to the Biochemical Journal, to Chemistry and Industry, and later, to Carbohydrate Research. The atmosphere of this period is conveyed in several review lectures given by Hirst for example, the fourteenth Pedler lecture to the Chemical Society (1955) on Some Problems in the Chemistry of the Hemicelluloses, the Presidential Addresses to the Chemical Society (1957 and 1958) on Some Aspects ofthe Chemistry of the Fructosans and Polysaccharides of the Marine Algae, respectively, on Plant Gums, at the IVth International Congress of Biochemistry, Vienna (1958), and the Bakerian Lecture to the Royal Society (1959) on Molecular Structure in the Polysaccharide Group. These lectures were delivered with a quiet authority, and the published manuscripts show meticulous attention to detail. 

Meningococcal vaccines have been comprehensively reviewed, distinguishing conventional polysaccharide vaccines, non-polysaccharide group B meningococcal vaccines, and conjugated meningococcal vaccines (1). 

Cellulose is another natural polymer belonging to the polysaccharides group. The chemical formula for cellulose is It has a chemical structure very... 

Integral membrane proteins are oriented in the membrane. In the plasma membrane, the extracellular part of the protein is often characterized by the presence of O-linked polysaccharide groups and disulfide (cystine) bridges... 

Few detailed studies have been made of the hydrodynamic behavior of polysaccharides. Theories concerning the solution behavior of polymers have met with only limited success in predicting polymer dimensions they have had the least success, perhaps, in their application to polysaccharides (as compared to synthetic polymers or proteins). The unique problems posed by the polysaccharide group make their study of great interest. Much more work of both a theoretical and practical nature will have to be carried out, particularly on charged polysaccharides, before a satisfactory treatment of their hydrodynamic behavior can be claimed. 

The chemical structure of lipid A of lipopolysaccharide isolated from Comamonas testosteroni was recently determined by lida et al. (1996) by means of methylation analysis, mass spectrometry and NMR. The lipid A backbone was found to consist of 6-0-(2-deoxy-2-amino-P-D-glucopyrano-syl)-2-deoxy-2-amino-alpha-D-glucose which was phosphorylated in positions 1 and 4. Hydroxyl groups at positions 4 and 6 were unsubstituted, and position 6 of the reducing terminal residue was identified as the attachment site of the polysaccharide group. Fatty acid distribution analysis and ES/MS of lipid A showed that positions 2,2, 3 and 3 of the sugar backbone were N-acylated or O-acylated by R-3-hydroxydecanoic acid and that the hydroxyl groups of the amide-linked residues attached to positions 2 and 2 were further O-acylated by tetradecanoic and dodecanoic acids, respectively. 

Naturally hydrophobic minerals such as graphite and talc are common gangue minerals found in sulfide ores and are difficult to separate due to their tendency to float together with valuable sulfide minerals. Despite the relatively successful use of the polysaccharide group of chemicals (e.g., dextrin, guar gum, and carboxymethyl cellulose) as flotation depressants for these naturally hydrophobic minerals, the nature of the adsorption processes remains in debate. Consequently, the adsorption of amphipathic solutes at naturally hydrophobic minerals such as coal and graphite, talc, and sulfur is of interest to many researchers, and a substantial amount of research has been discussed. 

Early workers considered the wall to be composed of three polysaccharide fractions namely cellulose, the hemicelluloses and the pectic polysaccharides. Grouped in the pectic fraction are all of the polysaccharides extracted from cell walls by hot water, ammonium oxalate, weak... 

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