Galactans synthesis

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. 

Synthesis of the arabinan domain of AG is less well characterized, but several of the arabi-nosyltransferases involved have been identified and characterized to different degrees. AftA, which has been purified, was shown in an in vitro assay to add the first Ar residue to the galactan domain of AG [271]. Two proteins, EmbA and EmbB were shown to be to be necessary for formation of the branched Ara6 motif, as absence of either protein either in vivo or in vitro resulted in a linear glycan (lacking branching at the 3 position of the 3,5-linked Ar ) [272]. However, the exact roles of these proteins in glycan formation are unknown. 

Using a similar approach, Gurjar described the synthesis of C-analog 88 of the disaccharide Q -ara/-(1 5)-ara/present in motif C of the arabino-galactan portion of Mycobacterium tuberculosis [50] (O Scheme 18). 

Satoh, T., et al., Synthesis, branched structure, and solution property of hyperbranched D-glucan and D-galactan. Macromolecules 38(10) 4202-4210, 2005. 

The basic mechanism is a disproportionation. Thus a disaccharide, such as sucrose, could give a triose and a free monosaccharide. Synthesis of a levan (i.e. a fructan) would be accompanied by the release of glucose, while the production of a dextran (i.e. a glucan) would liberate free fructose. By repeated transglycosylations of this type polymers arise. A similar mechanism occurs in the production of some plant fructans, but it is otherwise very rare in eukaryotes. Bacterial levans are usually much larger than their eukaryotic counterparts and other polymers produced in the same way include bacterial arabinans, xylans, galactans and glucans. 

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