Polysaccharide modification

These protruding structures may form catalytic sites or binding sites for small molecules. Remarkably, some polysaccharide modification enzymes of pathogenic bacteria are similar to enzymes of their host cells. For example, during cell development, pectin, a principal component in the primary cell wall of plants, is modified by its own pectin methylesterases that have /1-solenoid structures (Johansson et al, 2002) and in this respect, resemble pectin lyases secreted by bacteria to break down these structures (Lietzke et al., 1996). 

SCHEME 9.1 Biosynthesis of HS. (a) Elongation reactions to prepare the precursor polysaccharide backbone using both EXT1 and EXT2 enzymes, (b) Polysaccharide modifications. 

Inulin represents a renewable resource that can be modified to form a cross section of products, many of which have superior attributes to similar products derived from glucose polysaccharides. Modification of inulin expands the amount and type of functional properties available, opening the door to many new uses. Most of these compounds are readily biodegradable. To date, there are over 17,000 citations for inulin in chemistry abstracts. The chemical modification of inulin, pioneered by the work of Dorine Verraest and Herman van Bekkum in the Netherlands, and Takao Uchiyama in Japan, has been reviewed by Fuchs (1987), Verraest (1997), and Stevens et al. (2001). The following critiques a portion of the diverse range of potential chemical modifications of inulin. 

The polysaccharide modification strategy, the selected protein carrier and the conjugation methods are interdependent. The stracture of the carbohydrate-protein conjugate could be very diverse ranging from a neoglycoprotein t) e made from smaller fragments of the CPS linked... 

Chapter 15, written by H. N. Cheng and Qu-Ming Gu, discusses the application of biotransformations to polysaccharides modification. Polysaccharides are natural materials ideally suited for enzymatic modifications. The chapter introduces Upase-catalyzed and j8-galactosidase-catalyzed modifications of carbohydrate polymers. 

While the chemical structure of a polysaccharide is complex, most are composed of components with similar characteristics, which allow simultaneous manipulation of the entire polymer. Almost all polysaccharide modifications involve either cleaving an oxygen-carbon linkage between monomers or a reaction at a hydroxyl group. Reactivity at hydroxyls is reported either as the degree of substitution (DS), which is the average number of substitutions per monomer, or molar substitution (MS), which is the average number of moles of substituent per monomer. 

List five general types of polysaccharide modification and give an example of each. 

Alginate is a polymer composed of uronic acid monomers. While this acidic polysaccharide can be recovered from bacteria, the commercial source is brown seaweed. Both propylene glycol esterification and acetylation of the polymer cause an increase in the thickening capabilities of the gum. The acetylation of alginate by pseudomonal species demonstrates alternative biochemical methods for polysaccharide modification. 

McCormick C.L., Lichatowich D.K., Pelezo J.A., Anderson K.W., Homogeneous solirtion reactions of cellulose, chitin, and other polysaccharides, Modification of Natural Polymers, ACS Symposiitm Series No. 121, 1980, pp. 371-380. 

Yalpani, M.D. and HaU, L.D. 1984. Some chemical and analytical aspects of polysaccharide modifications. 3. Formation of branched-chain, soluble chitosan derivatives. Macwmolecular 17 272-281. 

Polysaccharides Modification approaches Description of reactions or products Potential applications... 

CHEMICAL MODIFICATION OF POLYSACCHARIDES - MODIFICATION OF DEXTRAN THROUGH INTERFACIAL CONDENSATION WITH ORGANOSTANNANE HALIDES... 

This chapter focuses on two subjects related to the field of mechanically stimulated reactions (1) chemical and photochemical CTOss-linking of HA in aqueous solutions and (2) advanced methods of solid-phase polysaccharide modification. From these processes, the cross-linked hyaluronic hydrogels acquire a number of valuable properties that significantly extend the range of their medical applications. 

MODIFICATION OF DEXTRAN THROUGH REACTION WITH ORGANOSTANNANE HALIDES AS A FUNCTION OF REACTION SYSTEM - A MODEL FOR POLYSACCHARIDE MODIFICATION... 

Chemistry - Polysaccharide modification is a well-known research area (5-7). A range of physical, enzymatic and chemical modifications are already described and easily applicable. Interesting modifications are cross-linking, esterification and introduction of reactive epoxy and acrylic groups as shown in Figure 1 ([Pg.292]

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