Reducing-terminal labeling

The substrate for this assay consists of hyaluronan with the reducing terminals labeled with the fluorogenic reagent 2-aminopyridine [144], It should be noted that the reaction products by hyaluronidase also contain oligosaccharides that do not contain the fluorogenic end group. As these products are not detectable by this method, not all scissions occurring in the substrate are detected. 

Takeda, Y, Maruta, N., Hizukuri, S. (1992). Examination of the structure of amylose by tritium labelling of the reducing terminal. Carbohydr. Res., 227, 113-120. 

Labeling starch with the 14C isotope of carbon at the anomeric position of the reducing terminal D-glucose unit was achieved by treatment with labeled cyanide followed by alkaline hydrolysis of the resulting cyanohydrin.17 Labeled maltose could be prepared from such labeled starch.18 In addition, starches modified by substitution might be labeled in the substituent being introduced, as shown by Kratz and Kaufmann,19 who prepared starch acetylsalicylate with 14C in the acetylsalicylate moiety. 

Both the macromolecular complexes and the adsorption on colloidal particles may be examined through study of the configurational properties of the terminally labeled Py-PEG-Py probe chain. One feature of interest is the degree to which the mobility of the labeled chain is reduced when it... 

Because oligosaccharides often branch, they can have more non-reducing than reducing terminals and the latter may anyway be blocked, for example by protein or lipid. Unfortunately, there is no simple method for labelling the non-reducing ends of chains and so their nature has often to be determined by indirect methods, such as methylation or oxidation (see below). 

Glycans can be removed by either chemical or enzymatic methods. The advantages of enzymatic release are that (a) no chemical alterations are made to the sugars and (b) the glycans retain a free reducing terminal that can easily be labeled with a fluorophore for highly sensitive detection. 

Erythrocyte-membrane Glycoproteins.—Human erythrocyte-membrane glycoprotein has been modified to a tryptic glycopeptide, which was desialylized by mild acid treatment. The non-reducing, terminal D-galactosyl residue of the glycopeptide was labelled by enzymic oxidation and reduction with sodium borotritide. 

After the introduction of C-labels into the protein or glycoprotein molecule, the ability to assign the resonances to specific carbon atoms is essential. In the case of glycophorin (see Fig. 1), it may readily be seen that 5 lysine residues and 1 N-terminal amino acid (per species) can be reduc-tively di[ C]methylated. This could theoretically lead to 6 resonances (or possibly more, if chemical-shift nonequivalence is observed for the dimethyl species) in the C spectrum of methylated glycophorin A. However, in most cases, the N, N -di[ C]methyllysine resonances all occur near, or at, the same frequency. It is then necessary to be able at least to assign, or... 

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