Polysaccharide Components

The separation of the polysaccharide components utilizes their different solubUities, polar groups, extents of branching, molecular weights, and molecular flexibUities and may be accompUshed batchwise or with easUy automated column techniques such as column or high performance Uquid chromatography. These procedures have been summarized in several reviews (3,141—143). 

The significance of phenoxy anions is well recognized in the isolation of kraft and other water-insoluble technical lignins by acid precipitation. The ioniza tion of phenoHc hydroxyl groups coupled with the reduction of molecular size renders native lignin soluble in the aqueous pulping solution, thus enabling its separation from the polysaccharide components of wood. 

The type-specific capsular polysaccharide from Streptococcus pneumoniae type 5 contains 2-acetamido-2,6-dideoxy- -D-x>>/o-hexopyranosyl-4-ulose residues (17). Sugar nucleotides of hexos-4-uloses are important intermediates in the transformation of sugars during the biosynthesis, but this is the only known example of such a sugar as a polysaccharide component. 

An intriguing question which is, of course, as yet impossible to answer, is why the bacteria synthesize so many and so diverse polysaccharide components. A common speculation is that this gives them an advantage in their protection against the bacteriophages. The latter have to develop specific... 

CelIulose.-Most biologists know that cellulose (l->4-linked P-D-glucan) is a polysaccharide component of all primary and secondary cell walls. Indeed, plant cell walls are... 

Figure 23.5 Oxidation of the polysaccharide components of HRP produces reactive aldehyde groups. Conjugation to avidin then may be done by reductive amination.

Figure 7.7 Structure of a generalized LPS molecule. LPS constitutes the major structural component of the outer membrane of Gram-negative bacteria. Although LPSs of different Gram-negative organisms differ in their chemical structure, each consists of a complex polysaccharide component, linked to a lipid component. Refer to text for specific details...

If the products of periodate oxidation are reduced with sodium borohy-dride, polyalcohols are produced which may be readily hydrolysed under mildly acidic conditions and the reaction products can be determined. The identification of these products gives considerable information about the linkages between the polysaccharide components and also their sequence in the overall structure. 

ITie work described in this chapter was initiated to determine the kinetics of enzymatic and microbial attack on blends containing starch and LDPE or starch, LDPE, and EAA. From the initial studies came a more general goal of identifying structural and compositional characteristics of blends (in general) that facilitate or retard degradation of the polysaccharide component. 

Tryptophan 108 is recognized to be an active site in promoting the hydrolysis of 3(l,4)-glycosidic linkages between amino sugar residues in polysaccharide components of the bacterial cell walls. This residue is shown to occupy the cleft as well as trjrptophan 62 and 63, and is in a hydrophobic region. Tryptophan residues 62 and 108 are indispensable for the action of lysozyme, and tryptophan 62 is known to be the only binding site for the complex formation (13). Oxidation of tryptophan-108 is expected... 

L-glycero-mannoheptose. The polysaccharide component of LPS may be divided into several structural domains. The inner (core) domains vary relatively little between LPS molecules isolated from different Gram-negative bacteria. The outer (O-specific) domain is usually bacterial strain-specific. 

Especially troublesome is bridging flocculation. It is therefore much more convenient to prepare emulsions with protein and polysaccharide components both present together in the aqueous medium before homogenization (Dickinson et al., 1998 Garti et al., 1999 Dickinson, 2008a). Moreover, in a direct comparison between the two techniques (Jourdain et al., 2008), it has been demonstrated that the experimentally more straightforward mixed emulsion approach can actually produce a better level of stability than the bilayer approach. 

The polysaccharide component of a lipopolysaccharide can be separated from the lipid component by selective hydrolysis of the glyco-sidic linkages of the 3-deoxy-D-manno-octulosonic acid residues connecting these two components. The conditions for the hydrolysis are mild, namely, 0.1 M acetic acid for 1.5 h at 100° (Ref. 18). Similar conditions, namely, M formic acid for 1 h at 100° or 0.05 M hydrogen chloride in methanol for 1 h at 85°, were used to split off the sialic acid residues from gangliosides.19,20... 

Lysozyme catalyzes the hydrolysis of the polysaccharide component of plant cell walls and synthetic polymers of j8(l — 4)-linked units of A-acetylglucosamine (NAG) (Chapter 1). It is expected from studies on nonenzymatic reactions that one of the intermediates in the hydrolytic reaction is a oxocarbenium ion in which the conformation of the glucopyranose ring changes from a full-chair to a sofa (half-chair) conformation (Chapter 1). The transition state analogue I, in which the lactone ring mimics the carbonium ion-like transition state n, binds tightly to lysozyme = 8.3 X 10 8M.10... 

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