Enzymic galactosylation

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. 

By these methods it could be shown that the enzymic galactosylation (Section 10.4.1) of tetrasaccharide 9,14 is selective for the GlcNAc terminal non-reducing unit bound at position 6 of galactose, for in the product pentasaccharide 9.1S, the anomeric proton of residue E is the only one displaced by 0.023 ppm (Augd et al. 1980). 

Reaction of 3, 5 -di- -butylsilanediyl derivatives of nucleosides with 2-(tri-methylsilyl) ethoxymethyl chloride (Sem chloride) gives the 2 -0-Sem derivatives 189, from which the 0-silyl protection can be removed by HF in pyridine. There have been further reports of the enzymic galactosylation of nucleosides at 0-5 using P-galactosidases. ... 

Reaction of glycosylmethylamines with aryldiazonium salts gives a class of compounds which, by acid catalysis or unknown factors of enzymic catalysis, generate glycosylmethyldiazonium ions. These, in turn, lose nitrogen, to yield highly electrophilic carbenium ions, as illustrated for the ) -d-galactosyl derivative 38 (see Scheme 8). 

The fact that ) -D-galactosidase from Escherichia coli is inactivated more rapidly in the absence of Mg than in its presence can be taken as evidence that the activation of the triazene 38, that is, formation of )5-D-galactosyl-methyldiazonium ion, proceeds without acid catalysis, because Mg is required for the proton-assisted catalysis of yS-D-galactoside hydrolysis by this enzyme.Additional evidence for the absence of acid catalysis in the de-... 

Mutant or knockout mice defective in specific enzymes involved in lipid synthesis have provided powerful tools for genetic analysis of lipid function in the nervous system. For example, disruption of the genes for ceramide galactosyl transferase or galactosyl ceramide sulfotransferase,... 

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