A -acetyllactosamine

This enzyme [EC 2.4.1.22] is a protein complex of two proteins (designated A and B) and catalyzes the reaction of UDP-galactose with D-glucose to generate UDP and lactose. In the absence of the ce-lactalbumin (protein B), the enzyme catalyzes the transfer of galactose from UDP-galactose to A-acetylglucosamine (Le., the activity of A-acetyllactosamine synthase, EC 2.4.1.90). 

In the synthesis of A-acetyllactosamin from lactose and A-acetylglucosamine with (3-galactosidase (289,290), the addition of 25 vol% of the water-miscible ionic liquid [MMIM][MeS04] to an aqueous system was found to effectively suppress the side reaction of secondary hydrolysis of the desired product. As a result, the product yield was increased from 30 to 60%. Product separation was improved, and the reuse of the enzymatic catalyst became possible. A kinetics investigation showed that the enzyme activity was not influenced by the presence of the ionic liquids. The enzyme was stable under the conditions employed, allowing its repeated use after filtration with a commercially available ultrafiltration membrane. 

Several fucosyltransferases have been isolated and used for in vitro synthesis. The Lewis A al,4-fucosyltransferase transfers unnatural fucose derivatives in from their GDP esters [23]. The enzyme al,3-fiicosyltransferase has been used to L-fucosylate the 3-position of the GlcNAc of A-acetyllactosamine and of sialyl a2,3-N-acetyllactosamine [24]. Several acceptor substrates with modifications in the GlcNAc residue could also be... 

Tejima et al. [218] found that partial tosylation of the 1,6-anhydrolactose derivative (310) gave the 2-0-tosyl derivative (311) in 25 % yield and this was converted into the epoxide (312) which could be converted into the anomeric azides (313) and hence into A-acetyllactosamine. Tejima et al. [219] have also prepared peracetyl lactosamine from the 1,6-anhydro derivative (314). 

H Chemical Shifts of Structural-reporter Groups of Constituent Monosaccharides for Asialo Di-, Tri-, and Tetra-antennary Glycopeptides of the A-Acetyllactosamine Type (Compounds 8, 9, and 13)... 

These findings help to differentiate between possible ways in which a-lactalbumin could influence the production of lactose. One of these, which, on the surface, appears plausible, is that a-lactalbumin might accept iV-acetyllactosamine as a substrate, this product having arisen from the enzymatic action of galactosyltransferase. The ensuing transglycosyl-ation, whereby lactose would be produced, could then account for the effect of a-lactalbumin in the presence of galactosyltransferase. Brew et al. (1968) showed, however, that a-lactalbumin has no affinity for A -acetyllactosamine and thus could not he involved in this reaction. 

An alternative possibility involves an induced conformational change in a-lactalhumin as a result of complexing with galactosyltransferase, so as to produce an affinity for A -acetyllactosamine. Although this explanation appears never to have heen ruled out, there would be no need to invoke it, since it is already known (Klee and Klee, 1970, 1972 Andrews, 1969 Fitzgerald et al., 1970a) that galactosyltransferase has the innate ability to carry out this reaction, even in the total absence of a-lactalbumin. 

Therefore, the simplest explanation for the action of a-lactalbumin and galactosyltransferase, as suggested by Browne et al. (1969), is that a-lactalbumin, in complexing with galactosyltransferase, modifies the conformational structure of the latter to produce a form of the enzyme that more readily catalyzes the production of lactose, and then does so in preference to A -acetyllactosamine. 

Murata T, Honda H, Hattori T, Usui T. Enzymatic synthesis of poly-A -acetyllactosamines as potential substrates for 23. 

Kaftzik N, Wasserscheid P, Kragl U. Use of ionic liquids to increase the yield and enzyme stability in the P-galactosidase catalysed synthesis of A -acetyllactosamine. Org. Proc. Res. Dev. 30. 2002 6 553-557. 

Lo-Guidice JM, Perini JM, Lafitte JJ, Ducourouble MP, Roussel 49. P, Lamblin G. Characterization of a sulfotransferase from human airways responsible for the 3-0-sulfation of terminal galactose 50. in A-acetyllactosamine-containing mucin carbohydrate chains. J. 

SCHEME 4.26 Synthesis of A -acetyllactosamine using glycosyl ester. 

Mohan, H, Gemma, E, Ruda, K, Oscarson, S, Efficient synthesis of spacer-linked dimers of A-acetyllactosamine using microwave-assisted pyridinium triflate-promoted glycosylations with oxazoline donors, Synlett, 1255-1256, 2003. 

Yuasa, H, Hindsgaul, O, Palcic, M M, Chemical-enzymatic synthesis of 5 -thio-A-acetyllactosamine the Hrst disaccharide with sulfur in the ring of the nonreducing sugar, J. Am. Chem. Soc., 114, 5891-5892, 1992. 

FIGURE 15.1 Three examples of A-linked carbohydrate chains found on glycoproteins oligomannose type (1), A-acetyllactosamine type (or complex type, 2) and hybrid type (3). The common pentasaccharide core is indicated. 

Biochemists who encounter a limited number of sugars, all having the pyranoid form, use an even more simplified nomenclature in their articles. They remove the D, L, p, and / and place the anomeric descriptor after the sugar symbol which gives, for A-acetyllactosamine,... 

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