Levan Polysaccharides

Levans are a group of ffuctans polymers of fructose forming a non-structural carbohydrate, which in the case of levans can themselves link together to form super-molecules comprising even hundreds of thousands (Fig. 2.14). 

Levans are synthesized in approximately all bacterial versions of fructan production, as well as being possible to produce by fracturing soybean mucilage. Levan, fructose-composed biopolymer of bacterial origin, has potential in biotechnology due to its prebiotic and immunostimulatory properties. It was suggested that the combination of levan and nutritionally important microelements in the form of NPs serves as a first step towards a novel 2 in 1 approach for food supplements to provide safe and efficient delivery of microelements for humans and support beneficial gut microbiota with nutritional oligosaccharides [68], 

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Dijkhuizen and coworkers identified and characterized a Lactobacillus levansucrase (systematic name sucrose [6)-P-D-fructofuranosyl-(2 ]n a-D-glucopyranoside 6-P-D-fructosyltransferase EC 2.4.1.10) from L. reuteri strain 121, which could produce a high molecular weight levan polysaccharide from fructose [207]. 

Yoo S-H, Yoon E J, Cha J, et al. (2004). Antitumor activity of levan polysaccharides from selected microorganisms. Internat. J. Biol. Macromol. 34 37-41. 

The elucidation of a levan polysaccharide produced by a novel halophilic isolate from soil samples taken from Camalti Saltern area in Turkey, Halomonas smyrniensis was achieved thanks to the glycosyl analysis. In particular, the microbial EPS was hydrolyzed with trifluoroacetic acid (0.5M TFA at temperature of 120°C for 1.5h) and subsequently analyzed by HPAE-PAD (High-Performance Anion-Exchange Chromatography Pulsed Amperometric Detection), a high-performance anion-exchange... 

Dextran, Hyaluronan, Curdlan, Levan Polysaccharides from Fungi (yeasts) ... 

Typical enzymes investigated for assisting with biofilm removal include proteases act to hydrolyse peptide bonds in proteins and peptides, amylases act to cleave glycosidic linkages in starch or glycogen, levan hydrolyases act to hydrolyse levan (polysaccharide). 

The above chemicals can be obtained by fermentation (qv) of other sugars. However, some compounds require sucrose as a unique feedstock. Examples are the polysaccharides dextran, alteman, andlevan, which are produced by specific strains of bacteria (48,54—56). Dextrans are used to make chromatographic separation media, and sulfated dextran derivatives are used as plasma extenders (41). Levans show promise as sweetness potentiators and, along with alteman, have potential as food thickeners and bulking agents in reduced-caloric foods (55,56) (see Carbohydrates). 

Among other polysaccharides studied were those elaborated by Neisseria per-flava (starch-type polysaccharide), Polytomella coeca (a starch richer in amy-lopectin than most natural starches), Pseudomonas morsprunorum (Wormald) (levan), Acetobacter acetigenum (cellulose), Aerobacter aerogenes (NCTC 8172) (Klebsiella Type 164), Bacillus megaterium. Bacterium pruni, and Bacterium prunicola (polyfructoses of the levan type). 

Polysaccharides. Part XXXIX. The Constitution of Certain Levans Formed by Bacterial Action, R. R. Lyne, S. Peat, and M. Stacey, J. Chem. Soc.. (1940) 237 -241. 

Two extracellular D-fructans, (2- 6)-linked S-D-fructofuranan or levan and the less common corresponding (2 l)-linked polysaccharide, of the inulin type, are elaborated by different bacteria. These polysaccharides are formed from sucrose by the action of sucrose fructosyltransferases. Terminal )S-D-fructofuranosyl groups are present in some bacterial heteropolysacchar-... 

Some antigens, such as type 3 pneumococcal polysaccharide, EPS and other polymeric substances such as dextrans (poly-D-glucose) and levan (poly-D-fructose) can induce antibody synthesis without the assistance of TH cells. These are known as T-independent (Ti) antigens. Only one class of immunoglobulin (IgM) is synthesized and there is a weak memory response. 

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. 

Bacterial cellulose, dextran and many other bacterial polysaccharides are composed entirely of D-glucose units the levans are condensation polymers of D-fructose. Dextrans from different species of Leuconostoc... 

The literature contains many references to the synthesis of levulosans by bacterial action. These substances are known as levans and so far they have all been found to be polysaccharides consisting of fructofura-nose residues in which the second or reducing carbon of one is joined to the sixth carbon of an adjacent residue. The levans have been discussed in a preceding chapter (page 225). 

It is of interest that similar enzymes, capable of exchanging glycosidic linkages, appear to be involved in the synthesis of some polysaccharides. Thus the polysaccharide dextran is formed from sucrose by enzyme preparations from Leuconostoc46 while the polysaccharide levan is produced from sucrose or raffinose by enzymes of other bacteria.49 The reactions may be written as follows ... 

The polysaccharide consisted entirely of fructose methylatlon analysis showed that the primary fructose linkages were P(2- 6) fructofuranosyl linkages. Carbon 13 nmr showed the product to be a levan type fructan. 

Fructans are polysaccharides composed of o-fructofuranose units. They are important in short-term energy reserves for grasses and some plants. Inulin, found in dahlias, and levans from grasses are examples of fructans. Levans are short linear polysaccharides composed of (3 2 1 linked fructose units as illustrated in structure 9.21. 

With all this war work progressing, a small group was still able to carry on with the normal carbohydrate research. Papers on starch, D-glucuronolactone, bacterial levans (with Stacey), and the polysaccharide associated with beta-amylase, all appeared in the Journals. 

Myeloma proteins occur in animal tumors of various types. The synthesis of these proteins can be induced in some experimental animals by injection of mineral oil, or the implantation of plastic discs.161 Myeloma proteins were shown to possess antibody activity, with specificity for different types of substances.161 Some of these proteins were found to combine with such carbohydrates as bacterial, cell-wall polysaccharides, lipopolysaccharides, dextrans, levans, and galactans.162 Myeloma proteins that combine with galactans or dextrans possess anti-galactan activity,163,164 or anti-dextran activity,165-167 and have been studied most extensively. 

The number of enzymes responsible for the formation of polysaccharides from sucrose is also restricted. The two best known enzymes that form polysaccharides from sucrose are the dextran, synthesized by the microorganism Leuconostoc mesenteroides (8) and related organisms, and the levan, produced from the same substrate by Acetobacter levanicum (9) and other species. 

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