Glycoconjugate with cell membrane

Saponins are a widespread class of bioactive compounds produced by many plant species. Saponins consist of a hydrophobic polycyclic triterpenes C-30 or steroidal C-27 sapogenin (aglycone/genin) and one or two (rarely three) hydrophilic glycoside moieties attached to backbone. Because of their amphiphilic properties, saponins are amphiphihc glycoconjugates which are able to interact with cell membranes and are also able to decrease the surface tension of an aqueous solution. This activity is the reason for the name saponin, derived from the Latin word sapo, which refers to the formation of a stable soap-like foam in aqueous solution [1,2]. 

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... 

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... 

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