DEAN B. COWIK AND RlCllAKD H. KOHKRTS 



17 



tions per minute) had an interspace volume of 23% with inulin as the test 

 substance. This value is in rough agreement with the 10 to 20% observed when 

 labeled proteins are used with E. coli. It can account for only one third of the 

 total water space observed. The remainder must be attributed to a volume 

 within the cells which is freely accessible to sulfate and phosphate. 



Permeability of Escherichia CoH to Potassium, Rubidium, Cesium and So- 

 dium. It has long been observed that many cells including E. coli have the 

 ability to concentrate potassium from the medium in which they grow and to 

 retain this potassium in spite of what appears to be high concentration gradi- 

 ents. Similar selective effects have also been noted for rubidium, cesium, and so- 

 dium. The permeability of the cell membrane was measured using these ions 

 to determine whether 'active transport' across an impermeable cell wall played 

 a part in establishing and maintaining such concentrations; or whether the 

 ions might enter the cells by diffusion and be retained by metabolic binding. 



I 

 Table 13. Immediate uptake of potassium, rubidium, cesium, and sodium by e. col 



a) Immediate uptake. Table 13 shows that under the usual conditions of 

 measurement a given volume of the E. coli cell contains a concentration of 

 the labeled compound equal to approximately 75% of the concentration of 

 that material in the medium. The water space so determined is not influenced 

 by either the differing concentrations or by the chemical properties of the four 

 ions under investigation. The similarity in the results suggests that the ob- 

 served uptake occurred by passive diffusion and that the quantity found in 

 the cells was not due to metabolic action. This conclusion is conlirmed by the 

 observation that the radioactivity is easily removed by washing the cells. 



b) Wash losses from resting cells. The outward passage of unbound potas- 

 sium, rubidium, cesium and sodium has been observed. Almost all of the radio- 

 activity taken up without metabolism is removed by washing the cells in 

 0.85% saline solution. No distinction was made by the cell among the various 

 substances used. 



c) Uptake during metabolism. Once having penetrated the cellular boundary 

 by diffusion, the ions of the environment are in immediate contact with the 

 reactive protoplasm of the cells, and metabolic binding may result. Such a 

 process is significantly different from that described above. The E. coli cell 



