Sialic acids modified

Figure 6.3 Synthesis of modified sugars with sialic acid aldolase mutants...

Sialic Acid Ethylenediamine Amine-Modified Sugar Residue... 

One of the most widely studied molecules from this group of adhesion proteins is N-CAM (B4). N-CAM contains type III fibronectin domains in addition to the immunoglobulin domains. N-CAM also forms covalent associations with poly-sialic acid. This modified form of N-CAM may exert a repulsive force through its high negative surface charge. This, in turn, would lessen cell adhesion and allow invasion. 

Yarema, K.J. 2001. New directions in carbohydrate engineering a metabolic substrate-based approach to modify the cell surface display of sialic acids. Bio techniques 31 384-393. 

Polythiophenes functionalized with monosaccharides have been evaluated for their ability to detect the influenza virus and E. coli (Baek et al. 2000). Copolymers of thiophene acetic acid 10 and carbohydrate-modified thiophenes 11 have been prepared via iron(III) chloride mediated polymerization. Addition of influenza virus to a sialic acid containing copolymer resulted in a blue shift of the polymer absorption maximum, resulting in an orange to red chromatic transition. Mannose-containing polythiophenes underwent color changes upon the addition of the lectin ConA or E. coli cells that contain cell surface mannose-binding receptors. A similar biotinylated pol5hhiophene afforded a streptavidin responsive material (Paid and Leclerc 1996). 

Fig. 17. Comparison of blood clearance of glycoproteins and asialoglycoproteins. Removal of terminal sialic acid moieties by enzyme (neuraminidase) exposes the penultimate galactose moieties. The modified macromolecules are removed from the bloodstream very fast due to their biorecognition by the asialoglycoprotein receptor on hepatocytes. Based on data from [250]...

Exact analysis of sialic acid is required in biologieal experiments where the biological role of sialic acid is frequently studied with the aid of sialidases, and the amount of sialic acids released is determined. This is also important for periodate oxidation studies on biological systems, where modification of sialic acids by periodate is only assumed, but chemical analysis of this effect by isolation and analysis of the modified sialic acids is seldom performed. These uncertainties in determinations of sialic acid can be overcome by the purification procedures already described. Furthermore, it must be stressed that unequivocal determination of the structure of a sialic acid, especially... 

The availability of, and analytical data for, these standards arc prerequisites for quantitative and qualitative analysis of the yield of modified sialic acids from periodate-borohydride-treated cells, and, correspondingly, for evaluation of the influence of such modifications on the biological behavior of cells. In such an experiment, related to a study of the life expectancy of rabbit erythrocytes, the simultaneous analysis of Neu5Ac, Neu5Gc, and their C7 and C8 analogs from rab-... 

S = protein or lipid core -[X] = oligosaccharide chain as sialic acid acceptor (taken, and modified, from Ref. 33).]... 

The first method has been widely applied. In some instances, removal of terminal sialic acid by using sialidases modified the function of the glycoprotein, but, in others, the function was not changed. The results of such investigations are listed in a review by L. Warren and coworkers.416... 

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