Reducing end, of polysaccharides

P-Amylase (EC 3.2.1.2) is an exo-enzyme, occurring in a few microbes. It hydrolyses a-l,4-glucoside linkages from the non-reducing end of polysaccharides. It causes the... 

Amine functionalities also may be created on polysaccharides (Section 4.3, this chapter). The reducing ends of carbohydrate molecules (or generated aldehydes) may be reacted with small diamine compounds to yield short alkylamine spacers that can be used for subsequent conjugation reactions. Hydrazide groups may be similarly created using f z s-hydrazide compounds (Sections 4.5 and 4.6, this chapter). 

In some instances, reducing sugars are present that can be reductively aminated without prior periodate treatment. A reducing end of a monosaccharide, a disaccharide, or a polysaccharide chain may be coupled to a diamine by reductive amination to yield an aminoalkyl derivative bound by a secondary amine linkage (Figure 1.96). Also see Section 4.6, this chapter, for an extensive discussion on carbohydrate modification techniques. 

KDO appears to be unique to Gram-negative bacteria. In the LPS that have been studied, KDO residues are situated at the reducing ends of the polysaccharide domains, linking them, by ketosidic bonds, to the fatty-acid-substituted 2-amino-2-deoxy-D-glucosyl disaccharides referred to as lipid A. Fig. 2 is a block diagram indicating the location of KDO in the LPS from Salmonella. 

An insertion mechanism for synthesis of cellulose. Using 14C "pulse and chase" labeling Han and Robyt found that new glucosyl units are added at the reducing ends of cellulose chains formed by cell membrane preparations from A. xylinum.135 This conclusion is in accord with the generalization that extracellular polysaccharides made by bacteria usually grow from the reducing end by an insertion mechanism that depends upon a polyprenyl alcohol present in the cell membrane.136 This lipid alcohol, often the C55... 

Following the identification of KDO as a constituent of LPS, studies by Osborn and her group ( 5) have revealed that, in LPS, KDO (or the KDO region ) is located at the reducing end of the polysaccharide chain, linking the core segment to lipid A. Later, the application of differential color reactions based on thiobarbituric acid (TBA tests) (6, 7) has led to the view that KDO is present, in LPS from Salmonella or E. coli, in the form of a branched trisaccharide (Fig. 1). In this model, a branchpoint KDO residue (KDO I), ketosidically-linked to the second glucosaminyl residue of lipid A, is substituted in position 4 or 5 by a... 

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