Of 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... 

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. 

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. 

Bettler E, Samain E, Chazalet V, Bosso C, Heyraud A, Joziasse DH, Wakarchuk WW, Imberty A, Geremia AR. The living factory in vivo production of A-acetyllactosamine containing carbohydrates in E. coli. Glycoconj J 1999 16 205-212. 

The practicability of such cyclic multi-enzyme preparations has been confirmed, e.g. for the synthesis of A -acetyllactosamine or the tetrasaccharide, sialyl Lewis, containing four different monosaccharide units. 

Figure 1. Examples of some GPI anchor structures from protozoan parasites (A-C), yeast (D) and mammals (E). The number of Gal residues in the T, brucei VSG anchor varies depending on the VSG variant [17]. The number of A -acetyllactosamines and sialic acids in the anchor of PARP (C) is variable, but the average composition of the side chain is Sialic Acid5-(Gal-GIcNAc)9 [16]. Branch points in the PARP GPI side chain are hypothetical. In the yeast anchor (D), only one of the two terminal Man residues is present. Many S. cerevisiae proteins contain a ceramide-based GPI (D) with the exception of some proteins such as Gaslp which contain a lyso- or diacylglycerol [15].

N. Le Marer and D. Stehelin, High alpha-2,6-sialylation of A-acetyllactosamine sequences in rai-transformed rat fibroblasts correlates with high invasive potential. Glycobiology, 5 (1995) 219-226. 

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