Leuconostoc, dextran synthesis

VedyashkinaTA, RevinW, Gogotov IN. Optimizing the conditions of dextran synthesis by the bacterium Leuconostoc mesenteroides grown in a molasses-containing medium. Appl Biochem Microbiol 2005 41 361-4. 

Synthesis of Branch Linkages in Leuconostoc mesenteroides B-512F Dextran... 159... 

As stated earlier (see p. 342), study of the cell-free, enzymic synthesis of dextran was initiated by Hehre and Sugg They demonstrated the ability of a cell-free extract of Leuconostoc mesenteroidea to catalyze the formation of dextran. The over-all reaction was represented by equation (1). In addi-... 

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. 

In commercial production, enzymes from a strain of Leuconostoc mesente-roides are used to synthesize dextran from sucrose, water, essential minerals, and vitamins (see under Synthesis, below). The native dextran so obtained is then carefully hydrolyzed to the proper molecular-weight average and recovered by fractional precipitation from solution with methanol (1 8). 

Evidence has been presented that the synthesis of a-(l -> 3)-branch linkages in Leuconostoc mesenteroides B-512 dextran occurs by nucleophilic attack of a hydroxy-group at C-3 of a free dextran molecule on C-1 of the reducing-end of a dextran-dextransucrase complex the dextran is displaced from the complex on forming an a-(l -> 3)-linkage. Thus, the synthesis of branched linkages does not require a separate branching enzyme. 

The synthesis of dextran from sucrose by a cell-free bacterial culture filtrate was first reported by Hehre in 1941 [152]. The genera of bacteria that are recognized to produce enzymes capable of synthesizing polysaccharides from sucrose are principally Leuconostoc and Streptococcus. These genera are gram positive, facultatively anaerobic cocci that are very closely related to each other. One notable difference between them is that the L. mesenteroides strains required sucrose in the growth medium to induce the formation of the enzyme(s), whereas the Streptococcus species did not require sucrose in the medium to form the enzymes [153]. 

Alcalde, M., Plou, F. J., Gomez de Segura, A., Remaud-Simeon, M., WUlemot, R. M., Monsan, P. Ballesteros, A. (1999). Immobilization of native and dextran-free dextransucrases from Leuconostoc mesenteroides NRRL B-512F for the synthesis of glucooligosaccharides Biotechnology Techniques, 13, 749-755. 

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