Monosaccharides labeling

Isotopic substitution and isotopic labelling 2-Carb-17. Unsaturated monosaccharides... 

As glycon affinity of glycosidases is generally low for monosaccharides (see Tables III and IV), problems with unspecific labeling may arise with glycon-derived inhibitors of high intrinsic reactivity which do not have additional features to provide enhanced affinity, for example, a suitably positioned... 

Maximum labelling of heparin with F-D was achieved at 5 hours at 25 °C, pH 8.4. In the case of heparin, the efficiency of labelling was not dependent on molecular weight, but solely a function of the ratio of the concentrations of labelling reagent to monosaccharide subunit in the reaction mixture. Similar results were encountered in the labelling of dextrans of different molecular weight (9). 

TES-32 is the most abundant single protein product secreted by the parasite. It is also heavily labelled by surface iodination of live larvae (Maizels et al., 1984, 1987), and is known by monoclonal antibody reactivity to be expressed in the cuticular matrix of the larval parasite (Page et al, 1992a). TES-32 was cloned by matching peptide sequence derived from gel-purified protein to an expressed sequence tag (EST) dataset of randomly selected clones from a larval cDNA library (Loukas et al., 1999). Because of the high level of expression of TES-32 mRNA, clones encoding this protein were repeatedly sequenced and deposited in the dataset (Tetteh et al., 1999). Full sequence determination showed a major domain with similarity to mammalian C-type (calcium-dependent) lectins (C-TLs), together with shorter N-terminal tracts rich in cysteine and threonine residues. Native TES-32 was then shown to bind to immobilized monosaccharides in a calcium-dependent manner (Loukas et al., 1999). 

Shanahan, M.F., Wadzinski, B.E., Lowndes, J.M., and Ruoho, A.E. (1985) Photoaffinity labeling of the human erythrocyte monosaccharide transporter with an aryl azide derivative of D-glucose. J. Biol. Chem. 260, 10897-10900. 

Synthesis. The synthases are present at the endomembrane system of the cell and have been isolated on membrane fractions prepared from the cells (5,6). The nucleoside diphosphate sugars which are used by the synthases are formed in the cytoplasm, and usually the epimerases and the other enzymes (e.g., dehydrogenases and decarboxylases) which interconvert them are also soluble and probably occur in the cytoplasm (14). Nevertheless some epimerases are membrane bound and this may be important for the regulation of the synthases which use the different epimers in a heteropolysaccharide. This is especially significant because the availability of the donor compounds at the site of the transglycosylases (the synthases) is of obvious importance for control of the synthesis. The synthases are located at the lumen side of the membrane and the nucleoside diphosphate sugars must therefore cross the membrane in order to take part in the reaction. Modulation of this transport mechanism is an obvious point for the control not only for the rate of synthesis but for the type of synthesis which occurs in the particular lumen of the membrane system. Obviously the synthase cannot function unless the donor molecule is transported to its active site and the transporters may only be present at certain regions within the endomembrane system. It has been observed that when intact cells are fed radioactive monosaccharides which will form and label polysaccharides, these cannot always be found at all the membrane sites within the cell where the synthase activities are known to occur (15). A possible reason for this difference may be the selection of precursors by the transport mechanism. 

The pathway of the biosynthesis of Neu5Ac demonstrates the origin of sialic acids from the cellular hexose and hexosamine pools. These sugars are, therefore, suitable components for the study of the biosynthesis of sialic acid. However, only ManNAc has been shown to be a relatively specific precursor of sialic acids, as may be seen from the distribution of radioactivity between the individual monosaccharides of glycoconjugates after incubation. Injections of radioactive ManNAc into animals, or incubation of surviving tissue slices or individual cells with this compound, give incorporation of label mainly into the sialic acids.226 227... 

Determination of oligosaccharide size is calculated from the mass of monosaccharide residues and the 2-AB label (Fig. 4.5.8). An example of the biantennary complex-type oligosaccharide is ... 

Benzoyl chlorides, like other acyl chlorides, react readily with alcohols to form the corresponding esters (259). The reaction requires 19 h to be completed, and it has been studied in the analysis of carbohydrates, aminosugars, and glycosides (260). Because the preparation of acyl derivatives of monosaccharides is difficult, phenyldimethylsilyl chloride has been also investigated as an alternative label (261). After dissolving the analytes in dimethylformamide and addition of... 

Physical or chemical modification of a substrate may additionally selectively affect transformation or uptake Keil and Kirchman (1992) compared the degradation of Rubisco uniformly labeled with 3H amino acids produced via in vitro translation to Rubisco that was reductively methylated with 3H-methane. Although both Rubisco preparations were hydrolyzed to lower molecular weights at approximately the same rate, little of the methylated protein was assimilated or respired. The presence of one substrate may also inhibit uptake of another, as has been demonstrated for anaerobic rumen bacteria. Transport and metabolism of the monosaccharides xylose and arabinose were strongly reduced in Ruminococcus albus in the presence of cellobiose (a disaccharide of glucose), likely because of repression of pentose utilization in the presence of the disaccharide. Glucose, in contrast, competitively inhibited xylose transport and showed noncompetitive inhibition of arabinose transport, likely because of inactivation of arabinose permease (Thurston et al., 1994). 

Phenyl-methyl-pyrazolone-labeled aldopentose and monosaccharides Nucleotides AMP. ADP, and ATP... 

EDC is also used to couple cattle serum albumin with a synthetic glycopeptide. DCC is used to activate hydroxyl groups in sugars. The coupling of nitroxide spin labeled species to monosaccharides is also accomplished using DCC. ... 

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