Enzymatic galactosylations

New sources of biocatalysts such as bovine al-3-galactosyltransferase produced by the baculovirus expression system are available and extend the vast field of enzymatic galactosylation. The enzyme transfers galactose with an a-linkage to the 3-position of the Gal residue in Fucal-2Gal 3l-OR [39]. 

Enzymatic galactosyl transfer from UDP-Gal to the 4-position of GIcNAc catalyzed by /J1-4 galactosyltransferase (/31,4-GalT)... 

L. Kroger, A. Scudlo, and J. Thiem, Subsequent enzymatic galactosylation and sialylation towards sialylated Thomsen-Friedenreich antigen components, Adv. Synth. Catal., 348 (2006) 1217—1227. 

A limited study conducted with this enzyme shows its high synthetic potential. Various non-natural Af-acyl residues (Table 4) are tolerated by this transferase, despite their close proximity to the site of enzymatic galactosylation [76]. A more thorough investigation may unveil an even broader synthetic scope of this biocatalyst. 

It has also been demonstrated that expensive substrates such as UDP-Gal can be readily prepared in situ by enzymatic conversion of the relatively inexpensive sugar nucleotide uridine 5 -diphospho-a-D-glucopyranose (UDP-Glc) using a UDP-Gal 4-epimerase enzyme. This system, coupled with an appropriate UDP-Gal transferase, provides more economic access to enzymatically galactosylated compounds. In these multienzyme systems, to increase enzyme efficiency and also avoid multiple fermentations for separate enzyme preparations, fusion proteins have been constructed that contain both the Gal-epimerase and Gal-transferase enzymes. The use of these fused enzyme systems has increased in the recent years as their catalysis of sequential reactions can have a kinetic advantage over the mixture of two separated enzymes since the product of the first enzyme travels a shorter distance before being captured by the next enzyme in the sequence. 

Kfen, V., Sedmera, P., Havlicek, V. and Fiserova, A. (1992) Enzymatic galactosylation of ergot alkaloids. Tetrahedron Lett., 33, 7233-7236. 

Scheme 11. Enzymatic galactosylation of a water-soluble GlcNAc-bearing polyacrylamide. Reagents i) CH2=CH-C0-NH2, TEMED, APS, H2O, room temp., 2 h ii) 1. HEPES buffer pH 6, 10 mM MnCh, UDP-Gal (1.5 eq.), GT, 37 °C, 24 h 2. gel filtration on Sephadex G-50, q.y.

Figure 6.3. Substrate-labeled fluorescent immunoassay for theophylline. (A) Effect of theophylline rabbit antiserum (O) and normal rabbit serum (A) on the enzymatic hydrolysis of 8-[3-(7-/l-galactosylcoumarin-3-carboxyamido)propyl]theophylline. (B) Effect of various concentrations of theophylline on the fluorescence resulting from enzymatic hydrolysis of 8-[3-(7-/)-galactosyl-coumarin-3-carboxyamido)propyI]theophylline. (Reprinted from Ref. 3, with permission from the American Association for Clinical Chemistry.)...

As an example of use of the chemico-enzymatic approach,the synthesis of the S. anatum polysaccharide (24) which consists of trisaccharide I units joined by eC-galactosyl-1— 6-mannose linkages, will be discussed. 

Collagen contains carbohydrate, predominantly in the form of glycosylated hydroxylysine residues, as O-galactosyl- -glucosyl side chains. The intermolecular crosslinks in collagen occur when the enzymatic oxidation of lysine residues by lysine oxidase spontaneously crosslink via aldimine and aldol bonds (10). 

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