Dextrans constitution

Structure analysis. Dextrans constitute a group of polysaccharides composed essentially of a(1- 6) linked glucoside units with a low proportion of branching (figure 1). they are produced by micro-organisms. Many different strains of bacteria exist which can enzymatically convert sucrose or starch to dextran. ... 

Polysaccharides. Part XXIX. Constitution of the Dextran Produced from Sucrose by Leuconostoc dextranicum (Belacoccus arabinosaceous Haemoiyticus), S. Peat, E. Schliichterer, and M. Stacey, /. Chem. Soc., (1939) 581-585. 

The microbial cells employed for the conversion have been seen to be enriched in the dextran rich bottom phase and also, the interface. The macromolecular substrates are also found located in the bottom phase. In fact, in one of the earlier studies on ethanol fermentation, starch alone constituted the lower phase of a two-phase system (.3). The solvent molecules are rather evenly distributed between the two phases. However, the partitioning behaviour of the solvent molecules can somewhat be changed by variations in the phase composition. Furthermore, a significant extraction of the solvent into the upper phase could be achieved by increasing the top to bottom phase volume ratios (1,11). Semicontinuous batch fermentations have been performed with the cells being recirculated in the bottom phase. After the conversion, the top phase with the product is removed and replaced by a fresh one along with more substrate. Alternatively, the phase is returned to the system after removal of the solvent e.g. by distillation (12,13). The... 

The DTA curves of several bacterial dextrans have been determined by Morita (142) in order to study certain relationships between the DTA curve peaks and their molecular constitution. 

The group of polysaccharides known as dextrans consists of a number of polysaccharides differing rather markedly in molecular constitution. All polysaccharides considered to be members of this class contain mainly (l->6)-a-D-glucosidic linkages. Other linkages that may be present are (l- 2)-, or, more commonly, (l->3)- and (l->4)-a-n-gluco-sidic linkages. 

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. ... 

Several species of streptococci are reported > to produce dextransucrases, although in many instances the n-glucans synthesized by these enzyme preparations have not been rigorously characterized as dextrans. The properties of streptococcal dextransucrases are somewhat different from those of Leuconostoc species synthetic activities are exhibited over a pH range of 5-8.5, and between 37 and 45°. Above all, the enzymes are constitutive and may, therefore, be obtained free from contamination by dextran. 

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