Polysaccharides enzymic synthesis

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. 

The enzymic synthesis of D-plant polysaccharides. Xylose isomerase has been found in Lactobacillus pento-... 

VI. Enzymic Synthesis of Bacterial Polysaccharides from Modified Precursors... 

Preparation of modified, bacterial polysaccharides having monosaccharide analogs inserted into the polymeric chain is of interest for study of the structure-properties relationship in these biopolymers. Incorporation of chemically prepared, modified, biosynthetic precursors of the polymers in enzymic reactions seems a promising approach for achieving this aim. Such an approach, which may be termed chemical-enzymic synthesis, has now been studied by our group,439-441 using O-specific polysaccharides (10-12) of Salmonella serogroups B and E as an example. 

Mode of isolation A. chemical synthesis B. enzymic synthesis C. degradation of oligosaccharide D. degradation of polysaccharide E. naturally occurring. 

A relatively small set of monomeric precursors can generate a wide range of polymers. This is most evident in the case of polypeptides and polynucleotides but the same principle applies to fatty acids, lipids and polysaccharides. The synthesis of these polymers is briefly sketched below [the enzymes catalysing key steps are indicated in square brackets for clarity]. 

Pozsgay V, Brisson JR, Jennings JH, Allen S, Paulson JC. Synthetic oligosaccharides related to group B streptococcal polysaccharides. 5. Combined chemical and enzymic synthesis of a pentasaccharide repeating unit of the capsular polysaccharide of type III group B Streptococcus and one- and two-dimensional NMR spectroscopic studies. J. Org. Chem., 1991 56 3377-3385. 

It appears that phosphorus is related to the formation of starch in the plant. Thus Hanes has synthesized a linear polysaccharide from a-D-glucopyranosc 1-phosphate (Cori ester) through the action of potato phosphorylase. Dunlap and Beckmann and likewise Cori have found that the B-fraction activates this enzymic synthesis, while the A-frac-tion is inactive. It has not been established whether this effect is due to the branched character of the B-fraction or to the presence of phosphate in its structure. 

The continuing interest of Bourne in the chemistry of polysaccharides and associated enzymes originated from the work of Haworth and Peat directed towards the enzymic synthesis and degradation of starch. The impetus for this work was given by the discovery, made by C. S. Hanes in 1940, that a phosphorylase isolated from the potato and pea effects the synthesis, from D-glucosyl phosphate, of starch, later shown (by Haworth, Heath, and Peat) to be amylose. In his first paper (with Haworth and Peat) in 1944, Bourne described the isolation of the Q-enzyme which, in conjunction with phosphorylase, effects the conversion of D-glucosyl phosphate into the major component of whole starch, namely, amylopectin. He had discovered the Q-enzyme in a fraction discarded by previous workers. Already, the quintessence of his mind was revealed in this work meticulous attention to detail, and perception of essentials. 

The Enzymic Synthesis and Degradation of Starch. Part VIII, The Use of Mixtures of P- and Q-Enzymes in the Synthesis of Starch-type Polysaccharides, S. A. Barker,... 

Chitin, a polymer of /3-D-(l- )-linked 2-acetamido-2-deoxy-D-glucose residues, is an important structural polysaccharide found predominantly in the exoskeletons of arthropods and in the cell walls of fungi. Its enzymic synthesis has been studied, by Glaser and Brown, in the mold Neurospora crassa. 

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