Biosynthesis of polysaccharides

Microorganisms are proficient in synthesizing a large number of polysaccharides. The pathways for their biosynthesis are similar to the procedures that take place for the formation bacterial cell wall. It is anticipated that there are well over 100 enzymatic reactions, directly or indirectly involved in the synfliesis of polysaccharides. Initially with glucose, suitable sugars (by transforming glucose to others) are included in the formation of polysaccharides. 

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Cell culture and biosynthesis of polysaccharides. The Helianthus annuus 1805 cell culture was initiated according to a previously described method (7), using germs of Helianthus annuus as an explant. 

Fig. 2. Time course of biosynthesis of polysaccharides from a cell suspension of Helianthus annuus 1805.

One of the most impressive findings has been the discovery of lipid intermediates in the biosynthesis of polysaccharides (see Refs. 2 and 465.) At least two structurally different types of these compounds exist the intermediate may be an isoprenoid alcohol ester of the glycosyl pyrophosphate or the analogous derivative of the glycosyl phosphate. Derivatives of the first type are formed by reaction between the sugar nucleotide and the alcohol phosphate, for example, undecaprenyl phosphate (120), which participates in the biosynthesis of Salmonella lipopolysaccharide.466... 

The sugar nucleotides (an uninformative name that has been used for glycosyl nucleotides, or more strictly, glycosyl esters of nucleoside di- or mono-phosphates) were discussed in this Series12 in 1973. Since then, accumulation of new data about these derivatives has continued, and now, about 35 representatives of this class are known to participate in the biosynthesis of polysaccharide chains of bacterial polymers (for a survey, see Ref. 13). These include glycosyl esters of uridine 5 -diphosphate (UDP), thymidine 5 -diphosphate (dTDP), guanosine 5 -diphosphate (GDP), cytidine 5 -diphosphate (CDP), cytidine 5 -monophosphate (CMP), and adenosine 5 -diphosphate (ADP). 

Stoddart RW (1984) Sugar nucleotides and cyclitols. In Stoddart RW The biosynthesis of polysaccharides. Croom Helm, London, p 27... 

Most microbial exopolysaccharides are apparently synthesized in-tracellularly. However, with various Leuconostoc, Streptococcus, and Bacillus species, such exopolysaccharides as dextran and levan can be formed by adding proper substrates that do not penetrate the cell membrane.216,217 Surprisingly little information is available about the biosynthesis of biopolymers of commercial value. However, as most of them are probably formed intracellularly, the process by which substrates enter microbial cells, where they are modified by various enzymic reactions and finally excreted in polymerized form into the medium, bears attention. Even with a lack of complete biosynthetic information, the results of research on related micro-organisms may be extrapolated to form a reasonable hypothesis for the biosynthesis of polysaccharides. 

The biosynthesis of most crystalline polymers is not well understood. The mechanism by which structural and insoluble proteins are assembled from monomers into structures such as cell membranes is almost completely unknown (33). A notable exception is the biosynthesis of polysaccharides which is believed to take place by phosphate displacement reactions of an activated subunit with the help of an enzyme system (33). The polymerization of bacterial cellulose is perhaps studied in most detail. Here the research has been helped because the reaction of monomer to crystalline polymer occurs extracellularly, remote from the bacterial surface (34). 

Stoddart, R.W. 1984. The Biosynthesis of Polysaccharides, London Croom Helm. 

In the final chapter, biofilm formation is reviewed, covering knowledge about structure and biosynthesis of polysaccharide intercellular adhesins (PIAs) which are central to biofilm formation. This comprehensive chapter explains all PIA-related principles of medical device-associated infections. 

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... 

The mechanism of the biosynthesis of polysaccharides has been reviewed in authoritative articles by Hassid and coworkers in this Volume and an earlier Volume of this Series. The present discussion will include only the biosynthesis of cellulose, because of its significance in the composition of plant cell-walls and because of the complexities that have been revealed by recent investigations. 

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