Phosphorylated Polysaccharides

Phosphorylation, with consequent modification of properties is possible in principle for any polysaccharide. Heavily phosphorylated derivatives of (10.20) such as (10.21) have not been well characterised, however. 

Various partially phosphorylated or crosslinked derivatives of (10.20) have been reported and a slight degree of phosphorylation is known to exist in some natural products (e.g. potato starch). Phosphorylation is now believed to play a central role in plant starch metabolism with both C3 and C6 positions being involved [17]. 

Phosphopolysaccharides (polysaccharide phosphate esters) of this kind occur frequently in living systems and in a number of important technological products. Many bacterial polysaccharides contain phosphate ester groups. In these the phosphate groups serve to link the saccharide rings to lipids or other biopolymer units as, for example, in the teichoic acids (Section 10.3). Phosphorylation is known to profoundly affect food properties (Chapter 12.4). 

A considerable number of phosphosaccharides have now been characterised by NMR, mass spectra, chromatographic or other techniques. Many of these phosphosaccharides have, however, been obtained only in minimal amounts via biochemical processes, and satisfactory chemical means for their bulk preparation are not yet available. 

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The Wassermann substance17 is prepared by extracting various animal organs, particularly beef heart, with alcohol, and its lipidal nature was early recognized. Pangborn174 described the preparation of a new phospholipid termed cardiolipin from beef heart and claimed that it was the essential constituent of the Wassermann substance. On hydrolysis it gave a fatty acid and a phosphorylated polysaccharide. In a later communication17 however, the carbohydrate constituent is stated... 

Fig. 32.—Possible Rotamers about the Oxygen to C-l Bond in a Phosphorylated Polysaccharide When Viewed Along the Bond.

Polyphosphates a. Phosphorylated polysaccharides Phosphomannans, phosphodextrans in vivo (mice, rabbits) Late/early 53, 54)... 

Other GPI-related lipids that do not anchor proteins are found on the surface of Leish-mania and Trypanosoma parasites. These include lipophosphoglycans (LPGs), glycoinosi-tolglycerolipids that anchor phosphorylated polysaccharides [40,41] low molecular mass... 

An acidic arabino-D-mannan isolated from M. smegmatis also contains two phosphate, six monoesterified succinate, and four ether-linked lactate groups per molecule.Saponification of the polysaccharide releases a phosphorylated- and a non-phosphorylated polysaccharide, the main features of which are the presence of chains of contiguous (1 5)-arabinofuranosyl residues attached to 0-4 of L-arabinopyranosyl residues. A serologically active D-arabino-D-mannan, isolated from the cells of M. tuberculosis, is composed of (1 5)-a-D-arabino-furanosyl residues and (1 6)- and (1 2)-D-mannopyranosyl residues. ... 

A similar mechanism can be invoked to explain the construction of some of the phosphorylated polysaccharides, where the transfer of alditol phosphate is replaced by a transfer of sugar phosphate. 

This relatively simple type of sequence is characteristic of the ribitol teichoic acids and many glycerol teichoic acids, as well as some related phosphorylated polysaccharides. Despite its simplicity the exact nature of the biosynthetic process is rather less well understood than is the case with the complex teichoic acids (above). 

Again, the simple phosphorylated polysaccharides grow by a mechanism similar to that of teichoic acids the basic scheme of assembly of the poly A/-acetylglucosamine phosphate of Staphylococcus lactis 2102 is shown in Figure 3.5 (Brooks and Baddiley, 1969). 

Sugars become available for the major metabolic pathways by being phosphorylated. Polysaccharide formation also requires phosphorylated sugars for de novo synthesis of glycosidic bonds. The tran lycosidations discussed previously depend upon preformed glycosides. Glucose becomes available for polysaccharide synthesis through the action of hexokinase... 

Another simple sugar that enters glycolysis at the same point as fructose is mannose, which occurs in many glycoproteins, glycolipids, and polysaccharides (Chapter 7). Mannose is also phosphorylated from ATP by hexokinase, and the mannose-6-phosphate thus produced is converted to fructose-6-phosphate by phosphomannoisomerase. 

Sodium carboxymethyl chitin and phosphoryl chitin had most evident influences on the crystallization of calcium phosphate from supersaturated solutions. They potently inhibited the growth of hydroxyapatite and retarded the rate of spontaneous calcium phosphate precipitation. These chitin derivatives were incorporated into the precipitate and influenced both the phase and morphology of the calcium phosphate formed (flaky precipitate resembling octacalcium phosphate instead of spherical clusters in the absence of polysaccharide) [175]. 

The acidic sugars discussed in this Section are glycuronic acids and glycu-losonic acids. Bacterial polysaccharides may also become acidic by substitution of sugar residues, for example by etherification with lactic acid, acetala-tion with pyruvic acid, or phosphorylation, and these possibilities will be discussed in the following Sections. A sugar that does not fall into any of... 

One of the recent fundamental advances in carbohydrate chemistry has been enzymic synthesis in vtiro this has now been realized with dextran8 and with levan.8 However, since phosphate sugars are not involved in the enzymic syntheses of these two bacterial polysaccharides, it is obvious that phosphorylation is just one process for the natural synthesis of polysaccharides. 

In addition to the coupled-signal method just described, phosphorylated carbon signals can be detected by use of praseodymium chloride, which displaces a- and /8-carbon resonances of a,/8-D-mannose 6-phosphate and a-D-mannosyl phosphate downfield, with little effect on other resonances. Europium chloride has analogous properties, except that the displacements are upfield. With certain polysaccharides, such as the O-phosphonomannan of Hansenula capsulata (29), the sig-... 

A oligosaccharide that cannot be degraded further by a polysaccharide hydrolase or polysaccharide phosphoryl-... 

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