Gram complex polysaccharides

FIGURE 9,24 Lipopolysaccharide (LPS) coats the outer membrane of Gram-uegative > bacteria. The lipid portion of the LPS is embedded iu the outer membrane and is linked to a complex polysaccharide. 

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...

Table II shows some of the constituents of the complex polysaccharides of gram-positive bacteria. Only the structures of certain Pneumococcus polysaccharides are known in more precise detail and these results can be summarised as follows ...

As shown in Figure 9.24, the outer membrane of Gram-negative bacteria is coated with a highly complex lipopolysaccharide, which consists of a lipid group (anchored in the outer membrane) joined to a polysaccharide made up of long chains with many different and characteristic repeating structures... 

Gram-negative bacteria have a more complex cell surface. The peptidoglycan layer is also the outer layer with respect to the cytoplasmic membrane. However, besides this, they have another outer polysaccharide membrane. This outer membrane is built out of lipopolysac-charides and lipoproteins, and can be a serious barrier for permeating hydrophilic molecules. 

In order to provide access here to information about other microbial polysaccharides, there follows a short review of reviews. The Chemical Nature of Bacterial Antigens is a source of information on the earlier work, and this was followed by two reviews - in the present Series in one of these, the bacterial homopolysaccharides were discussed and some of the more complex products were mentioned. A wide review of mucopolysaccharides and mucoproteins included references to many bacterial polysaccharides, and, subsequently, an account of the specific polysaccharides of the Gram-positive Pneumococcus, and of dextrans, levans, and products of Gram-negative forms appeared. There followed a comprehensive review of pneumococcal polysaccharides, and an account restricted to products of Mycobacterium tuberculosis appeared in 1948. A broad coverage was provided in 1950, in this case the products of pathogenic species being dealt with more particularly this work encompassed the basis of the more... 

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