The transport of amino acids, amino acid derivatives and ions across ion-exchange membranes.
The passage of inorganic salts, glucose, amino acids and peptides across polystyrene-backed double membranes (negative-positive fixed-charge junctions) was studied in a two-compartment cell and compared to a known cellular system, the Ehrlich-Lettre ascites carcinoma. It was concluded that passage proceeds by a 1:1 exchange of diffusing ions in the membrane. The more rapidly transported systems reflected an increased probability of exchange in all cases, as evidenced both by a saturation effect and by the degree to which the space charge was perturbed at the membrane. The amino group (as NH3+) of the amino acid involved in the exchange process was vital for transport. The presence of a second amino group, either ionized or as -NH2, accelerated the exchange. The presence of electron-attracting groups on the side chain or of a methyl group on the alpha carbon also facilitated passage. Cation dependence was seen. Passage was hindered by a second carboxyl group, an alcoholic group, or a lengthened side chain. Use of double membranes permits experimental electrode transport modelling and may facilitate design of a drug delivery system.