Active transport of sodium ions from the yeast cell

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Abstract
The excretion of Na ions from a "sodium-yeast" (Containing about 60 m[image]/kg) into 0.1 [image].-KC1 is nearly 3 times faster than into water and there is a nearly quantitative exchange of K for Na ions. When Na ions are excreted into water they are accompanied by bicarbonate and organic acid anions and the excretion ceases when about half the Na is excreted. There is no net excretion of Na ions into 0-l[image]-NaCl. When a Na-yeast is suspended in 1:20 of 0.1 [image].-NaCl, no net excretion of Na+ occurs over many hours. If suspensions are made with a series of solutions containing 0.1 [image]-NaCl and various concentrations of KC1, the excretion of Na+ increases with the K+ concentration of the suspending fluid, but this effect is maximal at a K+ concentration of 0.04[image]-KC1. When Na+ is excreted under similar con-ditions into 0.1.[image]-KC1 with NaCl ranging from zero to 1.0[image], little reduction in the rate of Na+ excretion occurs up to an external Na+ value of 0.2 M. At an external value of 0.43 [image] the Na excretion is approximately 50% that at zero Na+ concentration. The existence of 2 separate carriers for Na (outwards) and for K (inwards) is shown by the relative specificity of the transport in each case and the different action of inhibitors. Where Na ions (0.1 [image]) without any K ions are present in the suspending fluid, Na ions can be carried inwards on what may be regarded as normally the K carrier. The Na carrier excreting Na is inhibited by cyanide (0.002.[image]) and anoxia; it is not inhibited by azide (0.002[image]) or 2:4-dinitrophenol (0.002[image]). The K carrier involved in the uptake of K+ (or of Na+ if no K+ is present outside, and Na+ is present in quantity) is inhibited by anoxia, and by cyanide, azide and 2:4-dinitrophenol at con-centration of 0.002 [image]_. The results are shown to support strongly the theory of a "redox pump" for the biological per-formance of osmotic work. Various metallic ions can greatly inhibit the active excretion of Na ions into 0.1 [image]-KC1. Inhibition depends on the magnitude of the atomic number and on the presence of 18 electrons in the 2d outermost orbit, and not more than 2 in the outermost.