Biosynthesis of other polysaccharides

See also Biosynthesis of Glycoconjugates, Glycoproteins, Figure 9.28, Bacterial Cell Walls, Biosynthesis of Other Polysaccharides, UDP-N-Acetylglucosamine... 

See also Saccharides, Structural Polysaccharides, Oligosaccharides, Monosaccharide Nomenclature, Biosynthesis of Polysaccharides (from Chapter 16), Biosynthesis of Other Polysaccharides (from Chapter 16), Biosynthesis of Amino Sugars (from Chapter 16), Biosynthesis of... 

See also Biosynthesis of Other Polysaccharides, Biosynthesis of Glycoconjugates... 

Now let us consider the further conversion of PEP and of the triose phosphates to glucose 1-phosphate, the key intermediate in biosynthesis of other sugars and polysaccharides. The conversion of PEP to glucose 1-P represents a reversal of part of the glycolysis sequence. It is convenient to discuss this along with gluconeogenesis, the reversal of the complete glycolysis sequence from lactic acid. This is an essential part of the Cori cycle (Section F) in our own bodies, and the same process may be used to convert pyruvate derived from deamination of alanine or serine (Chapter 24) into carbohydrates. 

The biosynthesis of other O-specific polysaccharides has still not been investigated. The only additional example of demonstration of such a process is in the formation of (l->3)-a-D-galactan, the Ol antigen of Klebsiella.333 UDP-Gal was identified as the glycosyl donor in the reaction, but further details of the mechanism remain unclear. 

The block mechanism of chain assembly is characteristic for polymeric chains of the UGT type (see Salmonella O-specific polysaccharides 10-12 and 18) and the UG type (see capsular polysaccharides 25, 27, and 33), with UDP-activated sugars serving as initiators of chain growth. It seems rather safe to suggest that the biosynthesis of other polymers of these types occurs through a block mechanism as well. 

Synthesis of other polysaccharides involves many of the same mechanisms as for glycogen, particularly the use of nucleotide-linked sugars as activated biosynthetic intermediates and glycosyltransferase enzymes. Biosynthesis of several polysaccharides is described briefly below ... 

A book dealing with the surface carbohydrates of prokaryotic cells has discussed, among other topics, capsular polysaccharide antigens, immunological expression, the structures of bacterial polysaccharides,and the biosynthesis of capsular polysaccharides. ... 

In passing, it is worth noting that Astbury has recently presented a wholly admirable survey of the way in which, according to modem views, the optically pure and highly stereospecific loi -chain protein molecules may act as a template to direct the subsequent biosynthesis of other macro-molecular stmctmes, such as the polysaccharides and nucleic acids. It is perhaps permissible to quote one highly suggestive sentence apart from its closely reasoned context (6) ... 

Any of these three compounds can serve as the precursor for synthesis of other organic materials. A first stage in biosynthesis consists of those reactions by which 3-phosphoglycerate or PEP arise, whether it be from C02, formate, acetate, lipids, or polysaccharides. 

Other monosaccharide components (of bacterial polysaccharides) that are structurally related to D-ribose include D-riburonic acid,232 identified in the exocellular polysaccharide produced by a strain of Rhizobium meliloti, and D-arabinose, frequently present as the furanose, in polysaccharides of mycobacterial cell-wall.233,234 L-Xylose235,236 should probably be included in the group, as it may be derived from D-arabinose through epimerization at C-4. Biosynthesis of these monosaccharides was not investigated. 

Some results of studies on the biosynthesis of two other Klebsiella capsular polysaccharides have also been reported. In the case of type 2 specific polysaccharide336 (27), incorporation of the D-mannosyl group from GDP-Man into glycosyl-lipids and the polymer, catalyzed by a cell-envelope... 

By using mutants of maize and other species, progress has been made in understanding the pathways and enzymes involved in starch biosynthesis and the fine structure of starch polysaccharides. However, starch biosynthesis (Chapter 4) and granule formation are still not completely understood. Thus, integration of the information on polysaccharide biosynthesis (Section 3.6) with that on mutant effects (Section 3.7), is necessary to fully understand polysaccharide biosynthesis and to delineate the limits of this knowledge. 

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