Melibiose structure

Structural studies on the parent trisaccharide raffinose (see Section VII) are in complete harmony with the structure given for melibiose. It is difficult to see any feature of the melibiose structure which is still in doubt. 

The melibiose carrier MelB of E. coli is a well-studied sodium symport system. This carrier is of special interest, because it can also use protons or lithium ions for cotransport. The projection structure of MelB has been solved at 8 A resolution [107]. The 12 TM helices are arranged in an asymmetrical pattern similar to the previously solved structure of NhaA, which, however, follows an antiport mechanism (Na+ ions out of the cell and H+ into the cell). 

Hacksell, I., Rigaud, J. L., Purhonen, P., Pourcher, T., Hebert, H. and Leblanc, G. (2002). Projection structure at 8A resolution of the melibiose permease, an Na-sugar co-transporter from Escherichia coli, EMBO J., 21, 3569-3574. 

Draw the structures of a-sophorose, a-melibiose, and lactulose. Sophorose is two glucoses linked /3 (1-2). Melibiose is a galactose linked to a glucose by an a (1-6) bond. Lactulose is galactose linked /3 (1-4) to fructose. 

Melibiose [0-a-D-galactopyranosyl-(l—>6)-D-glucopyranose] is a constituent of the trisaccharide raffinose (see Section II,2,f), and is liberated on hydrolysis of the latter by invertase. A detailed, structural elucidation of this disaccharide was described by French.115 Melibiose is found in the exudates115 and nectaries204 of several plants, and is also found in the tissues of various plants.75,110,123 205-209 In Aconitum... 

The structure of epimelibiose was established58 through periodate oxidation, and by comparison of its osazone with that of melibiose (melting point, mixed melting point, and x-ray diffraction pattern). 

The exact structure of raffinose follows most simply from the fact that it is cleaved by mild acid hydrolysis, or by invertase action, to give D-fructose and melibiose,7 and by almond-emulsin a-D-galactopyrano-sidase to give D-galactose and sucrose.16... 

The hydrogen bonding in melibiose monohydrate includes a homodromic cycle. Cyclic hydrogen-bonding schemes are not common in mono- and disaccharides, but in the crystal structure of the epimeric a,yS-melibiose monohydrate, 6-0-a-D-galactopyranosyl-cr,/ -D-glucopyranose-H20 [MELIBM01] (Fig. 13.49),... 

The pure enzyme displayed the preference sucrose > raffinose > 1-kestose > nystose (in a ratio 100 24 10 6). Other carbohydrates such as turanose, cellobiose, melibiose, leucrose, methyl-a-D-glucopyranoside, and stachyose were also tested but their activity was negligible. Thus, the enzyme only recognized sugars containing a sucrose moiety in their chemical structure. The trisaccharide raffinose is equivalent to a sucrose molecule substituted at the C-6 hydroxyl group, whereas... 

Melibiose was similarly obtained through condensation with tetraacetyl-D-galactopyranosyl bromide in quinoline. This synthesis established the identity of the sugar with 6-(a-D-galactopyranosyl)-D-gluco-pyranose (XXVI), both structurally and configurationally. 

Raffinose is composed of three monosaccharides galactose, glucose, and fructose. It shares related structures with sucrose and melibiose. It is also related to stachyose, which possesses an additional (1—>6)-linked a-D-galactopyranosyl unit. 

The conventional mass spectra indicate no significant difference between melibiose (1 - 6) and gentiobiose (1 - 6), whose structures differ only by the stereochemistry of the disaccharide bond and of one OH group. 

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