N-acetyl-lactosamine

Among structurally diverse glycoprotein oligosaccharides, those containing repeating N-acetyl-lactosamine structures attract much attention in connection with various biological events, most notably as onco-differentiation markers. 

Galactosidase Bacillus circulans [MMIMJfMeSOd/bufier (one-phase) Synthesis of N-acetyl-lactosamine 38... 

Several CMP conjugates made available by this procedure could be transferred effectively to N-acetyl-lactosamine as an acceptor by using the a-2,6-sialyltrans-ferase from rat liver (Fig. 2.2.5.4). In this manner, several trisaccharides 74-77 could be generated carrying natural as well as non-natural sialic acids in good yields [47], limited so far only by the high cost of the commercial glycosyltransferase. 

Occasionally, the branchings are incomplete and the formation of the N-acetyl-lactosamine residues is only started in outline, as in the glycans of ovotransferrin (see Fig. 15), ovalbumin (see Fig. 16), and ovomucoid (see Fig. 18). In other instances, glycan structures such as have just been described are enriched with supplementary monosaccharide residues for example, the occurrence of disialyl groups [a-NeuAc-(2—>8)-a-NeuAc], and of /3-Gal-(l- 3) residues linked to the terminal galactosyl residues, has been demonstrated in different tissues and cell membranes,114,115 and in calf-thymocyte membranes,118 respectively. 

The conformation of some glycans has been studied with the aid of molecular models. For structures of the N-acetyl-lactosaminic type, having two antennae, two conformations are possible, the Y and the T. Results from X-ray diffraction studies favor the T conformation. Both conformations are in good agreement with the role of recognition signal that the glycans could play. 

Fig. 45.—Pathway of the Biosynthesis of Lipid-linked Oligosaccharide Precursor of the N-Acetyl-lactosaminic Type of Glycans, and of the Intermediary Glycopeptide. (See general reviews 126-136, 226, and 227.)...

L. Acarin, J.M. Vela, B. Gonzalez and B. Castellano, Demonstration of poly-N-acetyl lactosamine residues in ameboid and ramified microglial cells in rat brain by tomato lectin binding, J. Histochem. Cytochem. 42 (1994) 1033-1041. 

So far, we have never observed, by n.m.r. spectroscopy, oligosaccharides or glycopeptides bearing Fuc and NeuAc both linked to the same N-acetyllactosamine branch this is in agreement with the biosynthetic principle of mutual exclusion existing in transferring (1— 3)-1 inked a-fucosyl and (2— 6)-linked a-sialyl groups to the same N-acetyl lactosamine branch, as formulated by Hill and coworkers.88... 

Fig. 2. Reactions catalyzed by galactosyltransferase (GT). (a) The incorporation of galactose (Gal) into a (1—>4) linkage with JV-acelylglucosamine (NAG) to form N-acetyl-lactosamine (NAL). UDP, Uridine diphosphate, (b) Modification of the activity of GT by a-lactalbumin (a-LA) to convert it to a lactose synthase catalyzing the formation of lactose from UDP-Gal and glucose.

N-acetylglucosamine, terminal a-N-acetyl-lactosamine and terminal N-Acetyllactosamine residues in glycoproteins Terminal mannose a(2-3)-linked sialic acid... 

Following the enzymatic synthesis of CMP-Neu5Ac, isolated a2-6-sialyl-transferases could be used to introduce sialic acid to the N-acetyl lactosamine derivates a-f in position 6. This afforded a series of trisaccharide derivates Neu5Aca2-6 Gal l-4GlcNAc l-R. The unblocked trisaccharide a [55], the methyl glycoside b [56], the -Asn derivative c [57], the pentapeptide derivative d [58], the allyl e [59], and the pent-4-enyl glycoside f [48] can be prepared in convincing yields (Fig. 6). 

Attachment of neuraminic acid to )3-LacNAc-elymoclavine (11) yielding 19 was accomplished by the use of a-2,6-sialyltransferase from rat liver (EC 2.4.99.1) (Scheme 10). It was interesting that the affinity of the sialyltrans-ferase towards 11 was approximately 20% higher than that towards N-acetyl-lactosamine, the natural substrate of this enzyme. 

Fig. 94. A and B. Distribution of 3-fucosyl-N-acetyl-lactosamine (FAL)-immunoreactive Bergmann glial cells in adult mouse cerebellum. Note zonal distribution of immunoreactive neuroglia in molecular layer (MOL) in A. GCL, granular layer. Bars in A = 800 /tm, in B = 100 /jm. Courtesy of Dr. J.K. Mai, Department of Neuro-anatomy, Heinrich Heine University, Diisseldorf.

Complementary staining patterns were described for cytochrome oxidase in Saimiri sciureus and rat by Leclerc et al. (1990), for the distribution of P-path-immunoreactive (Edwards et al., 1989, see below) Purkinje cells in the mouse by Hawkes (1992), Leclerc et al. (1992) and Edwards et al. (1994) and for 3-fucosyl-N-acetyl-lactosamine (CDu) in mouse Bergmann glia (Fig. 94) (Bartsch and Mai, 1991 Marani and Mai, 1992). 

Bartsch D, Mai JK (1991) Distribution of the 3-fucosyl-N-acetyl-lactosamine (FAL) epitope in the adult mouse brain. Cell Tiss. Res., 263, 353-366. 

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