Polysaccharides

<p>Chitin forms the tough fibrous exoskeletons of insects, crustaceans and other arthropods, and, in addition to its presence in some fungi, it occurs in at least one alga. The structure of chitin is similar to that of cellulose but with glucose replaced with N-acetyl-D-glucosaminyl units linked β-D-(1,4) in a linear chain. Chitin is normally produced from the shells of lobster, crab or shrimp.</p>

<p>The fluorescence intensity of these Rhodamine B isothiocyanate-dextrans varies much less than with FITC-dextrans.</p>

<p>Glycogen is a highly branched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. It is the main storage form of glucose in the body.  In humans, glycogen is made and stored primarily in liver and muscle cells and functions as the second most important energy storage molecule to fat, which is held in adipose tissue. Glycogen is analogous to starch and has a structure similar to amylopectin, but is more extensively branched and compact than starch. It occurs as granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle.</p>

<p>Carboxymethyl cellulose is used in food as a viscosity modifier, thickener, to stabilise emulsions and are found in gluten-free and reduced-fat products. It is also a constituent of toothpaste, laxatives, diet pills, water-based paints, detergents, textile sizing, and various paper products.  In laundry detergents, it is used as a soil suspension polymer. It is also used in pharmaceuticals as a thickening agent and in the oil-drilling industry as a viscosity modifier and water-retaining agent.</p>

<p>Tara gum is a galactomannan that is obtained from the seeds of the tara shrub Caesalpinia spinosa which is a native of the northern regions of Africa and South America. The gum is described as having a backbone of (1,4)-linked β-D-mannopyranosyl units one third of which possess a single unit side chain of (1,6)-linked α-D-galactopyranose. The gum forms gels with carrageenan and xanthan in a similar manner to guar and locust bean gum. Currently, only small quantities of tara gum are sold for use as food thickeners and stabilisers.</p>

<p>Dextran sulphate is a dextran derivative whose ulcer (colitis) -causing properties were first reported in hamsters and extrapolated a few years later to mice and rats. The exact mechanisms through which dextran sulphate induces intestinal inflammation are unclear but may be the result of direct damage of the monolayer of epithelial cells in the colon, leading to the crossing of intestinal contents (for e.g. commensal bacteria and their products) into underlying tissue and therefore induction of inflammation.  The dextran sulphate sodium-induced ulceration model in laboratory animals has some advantages when compared to other animal models of colitis due to its simplicity and similarities to human inflammatory bowel disease. <br>MW is in the range of 40,000Da</p>

<p>Hyaluronic acid, a polysaccharide with alternating β (1,3) glucuronide and β (1,4) glucosamine residues labelled with 5-amino-fluorescein gives a yellow fibrous product, which is soluble in both water and electrolytes.  Fluorescein-labelled hyaluronic acid can be used as a probe to follow the fate of hyaluronan in vitro and greatly enhances the visualisation of the permeation of substrates through skin and other tissues. Other applications of fluorescein-labelled hyaluronic acid have been reported in cancer research.</p>

<p>Fluorescein isothiocyanate carboxymethyl dextran (FITC-CM Dextran) has been reported to provide a valuable carrier for nanoparticles of iron oxide.  These products provide a potent tool for contrast enhancement in magnetic resonance imaging.</p>

<p>A fucan sulphate found in brown marine algae (Phaeophyta-typically Fucus vesiculotus, Ascophyllum nodosum, Alaria and Macrocystis pyrifyra (illustrated) and has been shown to have anticoagulant activity. The main constituents are α-1,4 and α-1,2 linked L-fucose sulphates, although galactose also occurs and there are many variations of the basic structure found in different species of Phaeophyta.<br>The fucose content of this fucan is approx. 31% and it also contains galactose (approx. 2.2%), uronic acid (approx. 12.4%) and sulfate (approx. 32.5%).<br>The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.</p>

<p>An apiose-rich pectic polysaccharide zosterin is found in the sea grass Zostera marina and is typical of similar structures occurring in higher plants. The structure consists of an α-1,4-D-galactopyranosyluronan backbone substituted by 1,2-linked apiofuranose oligosaccharides and single apiose residues. The average molecular mass of the polysaccharide has been shown to be about 4100 Da with a low polydispersity.</p>

<p>Dextran is α-(1,6)-linked α-D-glucan with α-(1,3)-linked glucose branch points produced by fermentation of Leuconostoc mesenteroides via the action of the enzyme dextransucrase on sucrose.  The main use for native dextran is as an extender in blood transfusions and products having a range of sharp cut-off molecular weights are produced commercially for this and other applications.  A complex of iron with dextran, known as iron dextran, is used as a source of iron for baby piglets which are often anaemic at birth.</p>

<p>Pullulan is a glucan elaborated by the fungus Aureobasidium pullulans. The chemical structure is essentially repeating units of maltotriose joined by α-1,6 linkages. Pullulan dissolves readily in water to form stable, viscous solutions that do not gel. The polysaccharide can be moulded, made into fibres and forms clear soluble films. Applications are in foods as a low calorie ingredient and the polysaccharide forms water soluble films that have been used as seed coatings and to coat fruit. Pullulan can also be used in industrial applications as a binder, film former and in pharmaceutical applications.  Average MW is typically 100-200kDa.  Viscosity is ca 120 mm2/s.<br>The image was kindly provided by Dr. Chris Lawson.</p>

<p>A fucan sulphate found in brown marine algae (Phaeophyta-typically Fucus serratus, Ascophyllum nodosum (illustrated), Laminaria japonica and Macrocystis pyrifyra) and has been shown to have anticoagulant activity. The main constituents are α-1,4 and α-1,2 linked L-fucose sulphates although galactose also occurs and there are many variations of the basic structure found in different species of Phaeophyta.<br>The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.</p>

<p>Pectins are derived from citrus fruits such as lemons and limes. Amidated pectin is a modified form of pectin in which some of the galacturonic acid residues are converted with ammonia to amides. These pectins are more tolerant to varying calcium concentrations that occur in use and behave like low-ester pectins, need less of and are more tolerant to excess calcium. In addition, these gels are thermoreversible.</p>

<p>Dextran is α-(1,6)-linked α-D-glucan with α-(1,3)-linked glucose branch points produced by fermentation of Leuconostoc mesenteroides via the action of the enzyme dextransucrase on sucrose.  The main use for native dextran is as an extender in blood transfusions and products having a range of sharp cut-off molecular weights are produced commercially for this and other applications.  A complex of iron with dextran, known as iron dextran, is used as a source of iron for baby piglets which are often anaemic at birth.</p>

<p>Dextran sulphate is a dextran derivative whose ulcer (colitis) -causing properties were first reported in hamsters and extrapolated a few years later to mice and rats. The exact mechanisms through which dextran sulphate induces intestinal inflammation are unclear but may be the result of direct damage of the monolayer of epithelial cells in the colon, leading to the crossing of intestinal contents (for e.g. commensal bacteria and their products) into underlying tissue and therefore induction of inflammation.  The dextran sulphate sodium induced ulceration model in laboratory animals has some advantages, when compared to other animal models of colitis, due to its simplicity and similarities to human inflammatory bowel disease.</p>

<p>Isolichenan is a cold-water soluble (1,3)-(1,4)-α-D-glucan isolated from lichen Cetraria islandica to have MW of about 6-8 kDa. Lichens produce isolichenan-type polysaccharides with considerable variation in linkage ratios as well as MW, even within the same species. Occasionally these α-glucans can be branched at O2, O3 or O6. The immunomodulating activity of isolichenan was tested in in vitro phagocytosis and anti-complementary assays, and proved to be active in both cases.<br>The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.</p>

<p>A sulphated galactan from the red seaweeds (Gelidium spp.). The major gel-forming component agarose consisting of a linear chain of sequences of (1,3) linked β -D-galactopyranosyl units and (1,4 ) linkages to 3,6-anhydro-α-D-galactopyranosyl units. Gelation is via the formation of double helices.<br>Both Gelidium latifolium and Gelidium amansii are sources of both Agar (mixture of agarose and agaropectin) and Agarose. The images were kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.</p>

<p>Dextran sulphate is a dextran derivative whose ulcer (colitis) -causing properties were first reported in hamsters and extrapolated a few years later to mice and rats. The exact mechanisms through which dextran sulphate induces intestinal inflammation are unclear but may be the result of direct damage of the monolayer of epithelial cells in the colon, leading to the crossing of intestinal contents (for e.g. commensal bacteria and their products) into underlying tissue and therefore induction of inflammation.  The dextran sulphate sodium induced ulceration model in laboratory animals has some advantages, when compared to other animal models of colitis, due to its simplicity and similarities to human inflammatory bowel disease.</p>

<p>Larch arabinogalactan is extracted from the heartwood of the western larch Larix occidentalis. This compound has a backbone of 1,3-linked β-D-galactopyranosyl units each of which contains a side chain at position C-6. Arabinogalactans are used as emulsifiers, stabilizers and binders in the food, pharmaceutical and cosmetic industries, as low viscosity dietary fibres and as a prebiotic fibres.</p>