Abstract
Abstract Inhibition of uptake of cationic amino acids by certain neutral amino acids in the presence of alkali metal ions has been studied in the Ehrlich ascites tumor cell, in the rabbit reticulocyte and in yeast. When a hydroxyl group is introduced on carbon 4 (for the reticulocyte) or carbon 5 (for the Ehrlich cell) of straight chain amino acids, a sharp shift in the selectivity among the alkali metal ions occurs in favor of Na+ or of Na+ and K+ in the two animal cells. This shift is associated with attainment of a maximal interaction between the neutral amino acid and the alkali metal, and is taken to support a bridging by the ion between the amino acid and the receptor site. Although in both potassium-treated and glucose-treated yeast neutral amino acids also become much more inhibitory to cationic amino acid uptake in the presence of alkali metal ions, no augmentation has been observed on introduction of a side chain hydroxyl group, and selectivity among the ions is weak. Hence a bridging function is doubted for that organism. The ions exert additional inhibitory effects, independent of the presence of a neutral amino acid, which appear to be competitive with H+.
Highlights
When the w-hydroxyl group is on carbon 4 does a striking departure appear, K+ and Naf being far more effective and Li+ relatively low in effectiveness
Under this hypothesis our results specified the position taken by Naf, at first rather crudely by the limits set by the chain lengths of arginine, lysine, and their reactive homologues, and more closely later when the effects of the position of the hydroxyl group were seen [3]
This hypothesis is greatly strengthened by the present finding that dramatic changes in the selectivity among the alkali metal ions occur when the hydroxyl group is optimally positioned for the interaction
Summary
The methods of collecting the Ehrlich cell and rabbit reticulocytes and of using them to study transport have been described elsewhere [4, 9,10,11] and in the accompanying paper [12]. Incubation intervals were used short enough to permit initial rates to be approximated. Only from 60 to 80% of the red cell samples showed the typical reticulated morphology, most of the remainder were necessarily very young cells, functionally similar to those showing the typical staining. The cells were grown in the following medium with constant shaking at
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