Water-insoluble polysaccharides

Gum tragacanth is obtained from the large tap root and branches of a small perennial shmb found in the Middle East, especially Iran. Chemically, it is a mixture of water-insoluble polysaccharides. It is stable to heat, acidity, and aging, and is used extensively in pourable low calorie salad dressings. 

In 1954, Jeanes et al.5 reported the formation of glucan(s) by 96 strains of bacteria that were primarily Leuconostoc strains. (There is a question here as to whether they are strains or species, particularly with regard to the formation of different kinds of polysaccharides. The classification of the time was to place them into one species, mesenteroides, that had several different strains. This classification stands today.) The polysaccharides were characterized by various properties such as optical rotation, viscosity, periodate oxidation profile, and physical appearance after alcohol precipitation. The latter were observed to have different appearances, which were described by Jeanes et al.5 in various qualitative terms such as pasty, fluid, stringy, tough, long, short, flocculent, and so on. These differences in appearance provided an early suggestion of differences in structure (see Table I). Both water-soluble and water-insoluble polysaccharides were formed, and some strains seemed to form more than one kind of polysaccharide, as judged by their water solubility and by differences in the amount of alcohol needed to precipitate them. 

Hemicelluloses, the second group of plant-cell constituents, are water-insoluble polysaccharides. During the first stage of attack, hemicelluloses disappear more rapidly than cellulose. Later, hemicelluloses slow down in degradation owing to their heterogeneity. Fungi, bacteria, and actinomycetes are able to break down hemicelluloses by... 

McCabe and Smith" have observed that the cell-associated dextransucrase elaborated by S. mutans strain Kl-R is not bound to the cell-wall structure, but is derived from a water-soluble form of the enzyme that becomes incorporated into the (dextran) cell-capsule during dextran synthesis. As synthesis of dextran proceeds, the initially soluble enzyme is converted into two dextran-bound enzyme fractions, one bound reversibly and the other bound irreversibly to the water-insoluble polysaccharide. The soluble dextransucrase is progressively changed to the irreversibly bound enzyme and is inactivated. In terms of the reaction... 

Chitin and CS are a hydrophilic, hence, water-insoluble polysaccharides. The glass transition phenomenon could be also affected by moisture content, since it can work as a plasticizer. Plasticization occurs only in the amorphous region, such that the degree of hydration is quoted as moisture content in the amorphous region. In general, the following three states of water adsorbed on chitin and CS are distinguished ... 

A review on polysaccharide chemistry includes a section on water-insoluble polysaccharide immobilization of enzymes. 

Amylopectin a component of starch (the other is amylose). A. is a branched, water-insoluble polysaccharide (A/, 500,000-1,000,000) consisting of a main chain of a-l,4-linked D-glucose units with side chains (15-25 D-glucose units) attached a-1,6 to every 8th or 9th glucose. A. forms violet to red-violet inclusion compounds with iodine. It swells in water, and upon heating it forms a paste. 

Y. Peng, L. Zhang, Y. Zhang, X. Xu, J.F. Kennedy, Solution properties of water-insoluble polysaccharides from the mycelium of Ganoderma tsugae, Carbohydr. Pol, 59, 351-356, 2005. 

Several kinds of extracellular depolymerases have been purified and characterised from various microorganisms [187, 189,191, 195-197], All the depolymerases are comprised of an N-terminal catalytic domain, a C-terminal substrate binding domain, and a linker region connecting the two domains. Similar catalytic and binding domains have also been identified in other depolymerising enzymes that hydrolyse water-insoluble polysaccharides such as cellulose [198], xylan [198,199], and chitin [200], The catalytic domain contains a lipase box pentapeptide [Gly-Xi-Ser-X2-Gly] as the active site, which is common for serine hydrolase [201]. Further detailed aspects on the structure and mechanisms of PHA depolymerase (EC 3.1.1.76) can be found elsewhere [202]. 

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