Dextrans from sucrose, structure

A reducing disaccharide, consisting of D-glucose and D-fructose, named levjcrose 214) is formed in the reaction mixture to the extent of about 3 % during the synthesis of dextran from sucrose by an enzyme isolated from the microorganism Leuconostoc mesenteroides. Its specific rotation is [a]o —6.8° (in water) m.p. 161-162°C. Methylation studies show that its structure is 5-0-a-D-glucopyranosyl-D-fructopyranose. 

Structure of the Dextran Synthesised from Sucrose by a New Strain of Betacoccus arabinosa-ceous" M. Stacey and G. Swift, J. Chem. Soc., (1948) 1555-1559. 

Dextran is produced from sucrose by a number of bacteria the major ones being the nonpathogenic bacteria Leuconostoc mesenterodes and Leuconostoc dextranicum. As expected, the structure (and consequently the properties) of the dextran is determined by the particular strain that produces it. 

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. Polymers of glucose which have high molecular weights and chain-like structure produced from sucrose by certain bacteria. 

It has not been conclusively demonstrated that Lactobacilli elaborate dextransucrases, although the evidence at present available suggests that these enzymes may be constitutive to certain species of the genus. Hammond indicated that cell-free extracts of LactohadUus casei (32-1-H), an oral strain, synthesize from sucrose a polysaccharide serologically similar to dextran. LactohadUus RWM-13, a strain isolated from decomposing vegetable-matter, may produce a structure-bound, temperature-sensitive dextransucrase. ... 

Further, Figure 1 contains a companion infrared spectrum of the condensation product of dibutyltin dichloride and dextran. This spectrum appears strikingly similar to that of the product derived from sucrose. This is reasonable since the major structural difference is the presence of five membered rings in sucrose compared to only six membered rings present in dextran. 

L. mesenteroides B-1355 elaborates an enzyme that synthesizes a dextran identical in structure to B-512F dextran. It also elaborates a second enzyme that synthesizes a glucan from sucrose with an alternating sequence of a-1 6- and a-... 

Another extensively studied family of sucrose glucosyltransferases includes the extracellular enzymes from Leuconostoc and Streptococcus spp. Hehre (164) first indentified dextransucrase (sucrose 1,6-a-o-glucan 6-a-D-glucosyltransfer-ase, EC 2.4.1.5) in a culture supernatant of Leuconostoc mesenteroides and initiated structure and mechanism characterization. The enzyme became of practical interest because of the widespread application of dextran as a plasma support during World War II (165). Leuconostoc dextransucrase is sucrose induced (166), unlike the streptococcal enzymes (167), although expression of the latter varies considerably with culture conditions (168, 169). 

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