Enzymic Synthesis of Polysaccharides

The addition of the sugar residue to the receptor molecule may not involve a direct addition but may proceed through a glycosyl-enzyme complex. So far, only homoglycans have been prepared in the laboratory by use of enzymes. 

Although an oligosaccharide primer is helpful in initiating the formation of amylose from D-glucose 1-phosphate it is not clear whether a primer is of assistance in initiating all polysaccharide syntheses. Many of the en- 

Phosphorylases, which occur in a wide variety of sources, converts D-glu-cose 1-phosphate into an amylose type of polysaccharide with the formation of inorganic phosphate 166), The over-all reaction may be expressed as  

Amylomaltase 169), an enzyme isolated from Escherichia coli, synthesizes amylose-type molecules from maltose. Equilibrium is reached at about 60 % conversion, the amylose-type product having an average chain length of 10 D-glucose units  

However, if the D-glucose formed is destroyed by glucose dehydrogenase, the reaction goes to completion, and a polysaccharide is produced which closely resembles normal amylose. 

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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... 

Manganese is essential for the synthesis of chondroitin sulfate, a mucopolysaccharide which is an important component of bone cartilage. Manganese is also required to activate enzymes involved in the synthesis of polysaccharides and... 

Because the reaction is degradative, it requires a starch chain, and the product of a single event is a-Glc 1-P and a starch chain that has had one or more glucosyl residues removed. It is, therefore, not surprising that the reaction in the reverse synthetic direction also requires a starch chain or so-called primer. The primer hypothesis for the synthesis of polysaccharide was, thus, developed from an enzyme that was actually a degradative enzyme and not a synthetic enzyme. Nevertheless, the primer-dependent mechanism has been incorrectly assumed for the biosynthesis of starch for over 60 years. 

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. 

In addition to the synthesis of polysaccharides, the transglucosylation activity of GH family 13 amylosucrase from N. polysaccharea has been employed to modify amylo-polysaccharides, underlying the interest of this enzyme for the design of novel thickening agents, resistant starches, and original carbohydrate-based dendritic nanoparticles [73, 74]. 

In spite of the progress that has been made, several difficulties limit the use of cell-free enzymes for the synthesis of polysaccharides. The major problem is the complexity of many polysaccharide-synthesizing systems. Isolation, purification, and stabilization of the required enzymes is often difficult, as many enzymes lose activity when they are no longer membrane-associated. Enzyme isolation from eukaryotic sources is tedious, because of low cellular enzyme concentration. It is unlikely that cell-free enzymatic synthesis will provide better routes to most natural polysaccharides than do fermentation and isolation. The use of genetic engineering,... 

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