Polysaccharides

Low calcium heparin is a glycosaminoglycan, which occurs in many mammalian tissues and has important anticoagulant and thrombolytic properties. The chemical structure is composed mainly of two disaccharide repeating units A and B. A is L-iduronic acid 2-suplhate linked α-(1,4) to 2-deoxy-2-sulfamido-D-galactose 6-sulphate, while B is D-glucuronic acid β-(1,4) linked to 2-deoxy-2-sulfamido-D-glucose 6-sulphate.

In addition to the β-glucans from cereals, another group of β-glucans are found in the cell walls of yeast (Saccharomyces cerevisiae), bacteria and fungi, with significantly differing physicochemical properties dependent on source. Typically these β-glucans form a linear backbone with 1,3 β-glycosidic bonds but vary with respect to molecular mass, solubility, viscosity, branching structure, and gelation properties, causing diverse physiological effects in animals.  They are structural components in the cell walls of Saccharomyces cerevisiae and to provide stability, they have a few b-1,6 branch points that lock into other cell wall components (1 in 5 glucose residues). So in any extraction you get a few 1,6 linked glucose residues ~5%. The yeast and fungal β-glucans have been investigated for their ability to modulate the immune system. They are also used in various nutraceutical and cosmetic products, as texturing agents, and as fibre supplements. Their detailed molecular structures are key to the physical properties that they exhibit, such as water solubility, viscosity, gelation properties and physiological functions. The image was kindly provided by Dr. Chris Lawson.

In water, hydroxypropyl cellulose forms liquid crystals with many mesophases depending on concentration. These mesophases include isotropic, anisotropic, nematic and cholesteric, the latter resulting in many colors such as violet, green and red. Pharmaceutical applications include treatments for medical conditions such as dry eye syndrome (keratoconjunctivitis sicca), recurrent corneal erosions, decreased corneal sensitivity, exposure and neuroparalytic keratitis. It is also used as a binder in tablets. Hydroxypropylcellulose is also used as a thickener, a binder and emulsion stabiliser in foods with E number E463.  HPC is used as a support matrix for DNA separations by capillary and microchip electrophoresis.

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 (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 has many similarities to human inflammatory bowel disease.

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 Iiron with dextran, known as iron dextran, is used as a source of iron for baby piglets which are often anaemic at birth.

Gycosaminoglycan in many organs; joint lubricant and shock absorber

Welan gum is a microbial polysaccharide produced by a species of Alcaligenes and shows interesting rheological properties of use in the oil and agricultural industries. The structure is similar to gellan based on repeating glucose, rhamnose and glucuronic acid units but with a single side chain of either an α-L-rhamnopyranosyl or an α-L-mannopyranosyl unit linked (1,3) to the 4-O-substituted β-D-glucopyranosyl unit in the backbone.

Amylopectin is composed of between 2,000 to 200,000 glucose residues linked α (1→4) with α (1→6) branching. The molecule is highly branched, every 24 to 30 glucose units, resulting in a soluble molecule with many terminal residues. Starch is made of about 70% amylopectin by weight, though it varies depending on the source (higher in medium-grain rice to 100% in glutinous rice, waxy potato starch, waxy corn, and lower in long-grain rice, amylomaize, and russet potatoes).

Polymannuronic acid is produced from alginates by partial hydrolysis and chromatography of brown algae such as Laminaria digitata, Ascophyllum nodosum and Fucus spp. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.