Sialic acids glycoconjugates

Bayer, E.A., Ben-Hur, H., and Wilchek, M. (1988) Biocytin hydrazide—a selective label for sialic acids, galactose, and other sugars in glycoconjugates using avidin-biotin technology. Anal. Biochem. 170, 271-281. 

The sialic acid abbreviations used in the text are listed in Table I. They are drawn up on the basis of a Round Table discussion at the Fifth International Symposium on Glycoconjugates which took place at Kiel in 1979. 

Sialic acids occur in a-glycosidic linkage as components of oligosaccharides, polysaccharides, and glycoconjugates.19,41-44 As binding... 

A method for selective, radioactive labelling of sialic acids, especially in cell membranes, by mild oxidation with periodate followed by reduction with borotritide, has heen described by Gahmberg and Andersson.200 This procedure can be used either for isolation and characterization of the labelled, cell-surface glycoconjugates (see, for example, Ref. 201) or for autoradiography of tissues and cells (for example, erythrocytes).142... 

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... 

Because Neu5Ae has been found to be the precursor of all other sialic acids in mammalian systems,215-22a 2 11 it occurs, at least in small amounts, in glycoconjugates of tissues, where other types of sialic... 

Nonphysiological compounds have also been described as influencing the overall metabolism of sialic acid. Administration of ethanol (2 g/kg) to rats significantly decreases the sialic acid content of brain tissue.246 Convulsions induced by pentylenetetrazole (6,7,8,9-tetrahy-dro-5/f-tetrazoloazepine) are accompanied by a diminution in the rate of biosynthesis of polysialogangliosicles GT, and GQn, in rat brain.227 Such ManNAc analogs as 2-acetamido-l,3,4,6-tetra-0-acetyl-2-deoxy-D-mannopyranose or the 2-(trifluoroacetamido) derivative lead to a marked lowering of the incorporation of radioactivity from labelled ManNAc into glycoconjugate sialic acids of murine, erythroleukemia (Friend) cells.247... 

In contrast to the behavior of submandibular-gland sialyltrans-ferases, reports exist in the literature describing marked differences in the rate of transfer of different sialic acids to glycoconjugates. For instance, in embryonic chicken-brain, the occurrence of at least four si-... 

Sialic acid seems to be involved not only in regulation of the lifetime of soluble, serum glycoproteins but also of mammalian blood-cells. It was observed by Woodruff and Gesner474 that desialylated lymphocytes are reversibly trapped in liver they recirculate to the blood stream after about 24 h. This phenomenon was confinned with Listeria-specific, mouse T lymphocytes, which accumulated in the liver for one day, in contrast to the control cells.60 Reappearance of these cells in the circulation after one day may be explained by re-sialylation of their membrane glycoconjugates. This time period is in the range observed for the turnover of sialic acid in cell membranes, lasting, for example, for 33 h in rat-liver hepatocytes.475... 

In vivo, pyruvate lyases perform a catabolic function. The synthetically most interesting types are those involved in the degradation of sialic acids or the structurally related octulosonic acid KDO, which are higher sugars typically found in mammalian or bacterial glycoconjugates [62-64], respectively. Also, hexose or pentose catabolism may proceed via pyruvate cleavage from intermediate 2-keto-3-deoxy derivatives which result from dehydration of the corresponding aldonic acids. Since these aldol additions are freely reversible, the often unfavourable equilibrium constants require that reactions in the direction of synthesis have to be driven by an excess of one of the components, preferably pyruvate for economic reasons, in order to achieve a satisfactory conversion. 

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