D-Glucans dextrans

From the specific activities of gentlotetraitol and the reduced glucan, a number avarage molecular weight of about 38,500 was calculated for the P. oryzae cell wall p-D-glucan. Dextran T-20 was used as a control polysaccharide. 

Vacuum-ultraviolet, circular dichroism (v.u.c.d.) measurements have been made on films and solutions of linear D-glucan in a study of the conformation of dextran and its oligomers.123 Film formation of the linear dextran was accompanied by crystallization, and the v.u.c.d. band was observed at 165 nm, in contrast to nonlinear dextran films displaying a band at 177 nm. The difference was ascribed to hydrogen bonding of the ring-oxygen atom in the crystalline state. 

Enzymic hydrolysis of dextrans has provided information both on the linkage types and the disposition of different linkages as established by methylation. Since the publication of the earlier article,1 enzymic studies on Leuconostoc dextrans have continued, and investigations of Streptococcus a-D-glucans have shown that there are significant, structural differences between some of these and those of Leuconostoc spp. Reviews on dextrans have appeared.419,420... 

Hydrolysis by endo-( 1 -> 3)-a-D-glucanase has demonstrated the presence of consecutive a-(l - 3) linkages in a number of streptococcal a-D-glucans (mutans). Insoluble a-D-glucans produced by S. mutans OMZ 176 and OMZ65 were hydrolyzed by endo-(l- 3)-a-D-glucanase, whereas the soluble polysaccharides from the same sources, and dextran T-2000, were... 

Dextrans are glucose homopolysaccharides that have a considerable number of consecutive a-(l—>6) linkages in their major chains, usually more than 50% of the total linkages. These a-D-glucans also possess side-chains stemming from a-(1—>2), a-(l—>3), or a-(l—A) branch linkages. 

Her early endeavors to characterize the branch points in starch, and pursuit of the then-elusive a-(l — 6) linkage in starch, drew Dr. Jeanes to dextrans, since these polysaccharides contain a-(l — 6) linkages as their main structural feature. Dextrans are a family of D-glucans produced micro-bially from sucrose they contain from 50 to 100% a-(l — 6) linkages, depending on the microbial strain used. Dr. Jeanes became an authority on dextran sources, structures, and industrial applications. She published comprehensive bibliographies on dextran, the first in 1950 and another in 1978. These were a labor of love, produced with much effort before the days of automated data retrieval. 

Dextran (Fig. 3C) is a (1 6)-a-D-glucan with dominantly (1—>3)-ot-D-glucan branches and minor (1—>4)- and (1—>2)-ot-D-glucan branches, industrially produced from sucrose feedstocks, primarily by Leuco-nostoc mesenteroides but also by Streptococcus and Lactobacillus spp. Crude dextran and dextran fractions are soluble in aqueous medium and have been applied in a wide range of pharmaceutical/clinical and food applications for decades. 

Without doubt, concanavalin A (Con A) is the most celebrated and has proven to be one of the most useful of the plant lectins. Its physical chemical properties and carbohydratebinding properties are well documented in previous reviews [3,8]. Suffice it to note that it was first isolated and crystallized by Sumner and Howell in 1936, who showed it to require metal ions for its activity [74]. By virtue of its interaction with branched a-D-glucans, it is readily prepared by affinity chromatography on crossed-linked dextran (Sephadex) [75, 76]. A homotetramer at pH 7 (subunit M, = 26 500 Da) of Con A has been sequenced [77] and its crystal structure determined both in its native form [38,39] and complexed with methyl a-D-mannopyranoside [40] and Man(al-3)[Man(al-6)]Man[49]. 

In this Section, structural studies of the products of pyrolysis of the glucan, dextran, 1,6-anhydro- 3-D-glucopyranose (levoglucosan), and D-glucose will be briefly outlined. 

There are two main types of polysaccharide to be considered under this heading, the first being the dextrans, and the second, a-D-glucans containing solely, or mainly, (l->3)-a-D-glucosidic linkages. 

In this article, the term dextran will be used to describe preparations of D-glucans that contain substantial numbers of (1- 6)-linked a-n-gluco-pyranosyl residues. In order to attain an element of cohesion between its various Sections, the Chapter has been confined to dextrans produced by bacteria growing on a sucrose substrate. The great majority of dextrans fall into this group, although dextrans have been synthesized from other substrates by micro-organisms, and a chemical synthesis of an essentially unbranched dextran has been reported. ... 

Dextran is the polysaccharide produced by several species of the genus Leuconostoc. Structurally, dextrans are D-glucans in which 6-linkages are predominant. 

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