Galactosyl -galactose

FIGURE 6.20 A disaccharide of galactose and glucose is covalently linked to the 5-hydroxyl group of hydroxylysines in collagen by the combined action of the enzymes galactosyl transferase and glucosyl transferase. 

Alternatively, penta-O-acetyl-galactose can be converted to the known 2,3,4,6-tetra-O-acetylgalactopyranosyl azide59 which after treatment with sodium methoxide in methanol and subsequent pivaloylation with pivaloyl chloride in pyridine, also furnishes the O-pivaloylated galactosyl azide60. 

The slightly galactosylated mannans are essentially linear polymers. As a result of their cellulose-like (1 4)-/3-D-mannan backbone, they tend towards self-association, insolubility, and crystallinity. Crystallographic study of C. spectabilis seed GaM [180] with a Man Gal ratio 2.65 1 suggested an orthorhombic unit cell with lattice constants of a = 9.12, b = 25.63, and c = 10.28 the dimension b was shown to be sensitive to the degree of galactose substitution and the hydration conditions [180 and references therein, [191]]. 

In the case of arAGP (see Fig. 3A), peaks 2 and 4 correspond to C-1 of Gal/ (1 —>4) substituted at 0-6 and 0-3, respectively, by75-76 a-D-NeuAc, whereas peak 3 corresponds mainly29 to unsubstituted Gal/ (1—>4). Thus, the ratios between the three types of galactosyl residue could be obtained by appropriate integration. They were found to be 5 3 2 for the C-6, C-3, and unsubstituted galactose residues, as opposed to the reported ratios of 2 2 1 for C-6, C-4, and C-3 of substituted galactose... 

Structure 34 was proposed for a trisaccharide composed of d-glucose, D-galactose, and 2-acetamido-2-deoxy-D-galactose residues. The D-glucosyl group and the D-galactosyl residues are the same as in disaccharide 32. That the 2-acetamido-2-deoxy-D-galactose residue is linked to 0-3 was indicated by color reactions and the fact that this... 

The D-galactosyl residues are the same as in disaccharide 33, and the fact that ribitol is substituted at 0-2 was evident from the methyl-ation analysis. Finally, a nonreducing tetrasaccharide was obtained, containing D-galactose, 2-acetamido-2-deoxy-D-galactose, and ribitol residues in the proportions 2 1 1. From these results, and periodate-oxidation studies, structure 36 was proposed for the neutral hexa-saccharide. 

Monosaccharide attachment to some of the hydroxylysine residues within the a chains occurs at this stage as galactose (gal) and glucose (glc) residues are added by specific galactosyl transferase and glucosyl transferases. The carbohydrates are attached as single monosaccharides or as gal-glc disaccharides. 

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