Linked Polysaccharides

Carbohydrate chains of teichuronic acids and neutral polysaccharides linked to the carbohydrate chains of peptidoglycans are fragments of macromolecules of Gram-positive cell-wall. Only two examples of the biosynthesis of these polymers have been studied in detail. Evidence for both block and monomeric mechanisms of the chain assembly was obtained. 

Being composed of linear chains of a highly crystalline polysaccharide, linked by 1 — 4, D-anhydroglucopyranose bonds that are hydrolyzed with relative ease, cellulose has long been the subject of partial acid hydrolysis to mixtures of hydrocolloid particles [65]. Hydrolysis of the disordered (paracrystalline) regions of cellulose liberates highly crystalline particles with dimensions in the 50 to 100 pm range. When dissolved in a suitable cellulose solvent, these par-... 

The characteristic components of the cytoplasmic membrane of Gram-positive bacteria are the amphiphilic macromolecules lipoglycan and lipoteichoic acid [39,40] (O Fig. 8). Lipotei-choic acids possess in their saccharide chain alditol phosphates as characteristic components, whereas lipoglycans are linear or branched polysaccharides linked to diacylglycerol. These molecules may be further substituted by phosphoglycerol residues. Since lipoteichoic acids and lipoglycans are not found in the same bacterium they are believed to replace each other... 

Carbohydrates and fatty acids are also necessary for rapid and good-quality skin regeneration. The extracellular matrix is made up of glycosaminoglycans and proteoglycans, which are polysaccharides linked to proteins. Omega-6 fatty acids are essential for cell membrane formation. Supplements of linoleic and linolenic acid can be recommended when the patient s blood is not properly balanced. ... 

The relatively small region of allowable values of tp and j/ in polysaccharides linked between rings makes the wormlike chain model realistic for them. The polymer behaves as a random flight one over contour lengths S Lp, but as a stiff rod if S Lp. Persistence lengths can be fairly large 350 50 A for xanthan gum, 80-100 A for alginate or hyaluronate. ... 

According to Scheme 1, the last reaction in the synthesis of LPS is the joining of completed O side-chain to the core. This unusual reaction, involving the joining of two macromolecules, was found to occur in a cell-free system. O Side-chains linked to P-ACL were generated in vitro in a cell-envelope preparation from a core-deficient mutant, and this particulate preparation was incubated with an exogenous, core LPS this resulted in eflScient transfer of the O side-chain to the core, a transfer catalyzed by an enzyme or enzymes present in the cell-envelope fraction. Unfortunately, a satisfactory method is not yet known for the extraction of O side-chain polysaccharide linked to PP-ACL, and further resolution of this system has not yet been achieved. 

At the request of the Codex Committee on Food Additives and Contaminants at its thirty-eighth session (Codex Alimentarius Commission, 2006), the Committee evaluated the enzyme isoamylase (glycogen a-1,6-glucanohydrolase EC 3.2.1.68). Isoamylase catalyses the hydrolysis of 1,6-a-D-glucosidic branch linkages in glycogen, amylopectin and their beta-limit dextrine. It has no or only limited activity on linear polysaccharides linked by a-1,6-glycosidic bonds (e.g. pullulan) and on alpha-limit dextrine. 

Modification of Polysaccharides and Oligosaccharides, and Uses of Modified Polysaccharides and Oligosaccharides Introduction.—A book entitled Polysaccharide Shapes has discussed how the units of polysaccharides link together to confer a unique set of properties on the chain. Papers presented at a symposium on the thermal uses and properties of carbohydrates and lignins have covered some aspects of the pyrolysis of natural polysaccharides. ... 

Cinelli, L.P., Vilela-Silva, A.-C.E.S., and Mourao, P.A.S. (2009) Seminal fluid from sea urchin Lytechinus variegatus) contains complex sulfated polysaccharides linked to protein. Comp. Biochem. Physiol., 154B,108-112. 

Amylose, a natural linear polysaccharide linked through (1 4)-a-glycosidic linkages (Figure 1), is one component of starch, which has been studied for many years in the materials research field because of its low cost, biodegradabilily, and renewabilily [1]. 

Arabinan. This highly soluble polymer is found in the extracts of many fmits and seeds, in the boiling water extracts of pine wood (127), in the extracts of marshmallow roots (A/t/jaea officina/is) (128), and aspen (63) and willow (Sa/ix a/ba F) (129) bark. Because arabinan can be isolated from mildly degraded pectin fractions, it is often difficult to determine whether it is a hemiceUulose or a labile fragment of a larger polysaccharide and/or lignin complex. Arabinans have a complex stmcture composed almost entirely of 5-linked a-L-arabinofuranosyl units with similar residues linked to them at C-2 and/or C-3 and is soluble in 70% aqueous methanol solution. 

Cross-Linking of Polyols. Polyols such as natural polysaccharides, eg, cellulose, starch, guar gum and their derivatives, and polyvinyl alcohol and its derivatives can be cross-linked by organic titanates. 

The distinctions between these homopolymers arise from the different ways in which the monomer units are hooked together in polyacetal chains. Starch (qv), plant nutrient material, is composed of two polysaccharides a-amylose and amylopectin. cx-Amylose is linear because of exclusive a (1 — 4) linkages, whereas amylopectin is branched because of the presence of a (1 — 6) as well as a (1 — 4) links. The terms linear and branched refer only to primary stmcture. 

Plant stmctural material is the polysaccharide cellulose, which is a linear P (1 — 4) linked polymer. Some stmctural polysaccharides iacorporate nitrogen iato thek molecular stmcture an example is chitin, the material which comprises the hard exoskeletons of kisects and cmstaceans. Chitki is a cellulose derivative whereki the OH at C-2 is replaced by an acetylated amino group (—NHCOCH ). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both ki monomer units and the nature of thek linkages. 

Certain cereal grains, especiaUy wheat and rye, contain hemicelluloselike arabinoxylans [9040-27-1], commonly caUed pentosans. Wheat flour pentosans are divided into two types water-soluble and water-insoluble arabinoxylans, which respectively constitute - 1.1 1.6% and 0.4—0.7% of the total flour. These polysaccharides have functional roles in dough development and baking performance. The water-soluble wheat-flour arabinoxylans consist of a (1 — 4)-linked chain of P-D-xylopyranosyl units substituted at 0-2 and/or 0-3 with single-unit a-L-arabinofuranosyl units. Preparations from each source consist of a family of molecules of various molecular weights and xyl ara ratios. 

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