Transport of Ions, Amino Acids, and Proteins

Conflicting results were obtained in the study of the influence of sialic acid on the flow of ions through the cell membrane Click and Githens (1965) observed a sharp response of the K+ ions to the removal of sialic acid with neuraminidase in L1210 leukemia cells, whereas the transport of Na ions was only slightly inhibited the transport of ions was inhibited regardless of the direction of flow. In Ehrlich ascites cells, however, removal of sialic acid residues with neuraminidase did not alter the content of Na and ions in the cells. Only a very small reduction in the unidirectional fluxes of K ions was observed after neuraminidase treatment. These observations led Weiss and Levinson (1969) to conclude that anionic sites on the cell membrane were not of major importance in regulating the intracellular concentration of Na and K ions or the unidirectional, transmembrane flux of ions. 

Sialic acid residues were found to be important in the transport of amino acids and proteins in cancer cells, since neuraminidase treatment of HeLa cells decreased the net accumulation of a-aminoisobutyric acid without altering the rate of efflux of preloaded cells (Brown and Michael, 1969), and the same treatment of L1210 leukemia cells inhibited the outward flow of proteins without influencing lysis or the release of nucleosides or sugars. Some relative specificity in the release of proteins was shown by disk-gel electrophoresis (Click et aL, 1966). 

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