12 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



bolically bound radioactivity is subtracted from the total quantity of radio- 

 activity removed by the cells, it is found that the quantity of diffusible sulfate 

 was 15.4% of the original radioactivity of the medium. This corresponds to a 

 water space of 64% of the total cell volume. 



Since 61% of the initial radioactivity is lost from the immersion fluid by 

 metabolic incorporation, only 39% is left to equilibrate by diffusion between 

 cell and environment. In addition, continuing metabolism of the cells during 

 the wash procedures may markedly reduce the diffusible sulfate content ob- 

 served in wash analysis. This may account for the lower value (64%) deter- 

 mined for the water space in this experiment. 



Table 6. Immediate radiosulfate 

 uptake by t. utilis and e. coli 



* Sulfur concentration of original medium 

 was 0.1 /ig/ml. 



Table 7. Immediate sulfate uptake by 

 T. utilis 



* Sulfur concentration of original medium, 

 i.o mg/ml. 



These difficulties may be reduced by several precautions, as the results of 

 table 7 show. In this experiment yeast cells kept in the stationary phase for 

 two days were used. Carrier sulfate at a high concentration of i.o mg sulfur/ 

 ml of 0.85% saline solution was used in the original medium. Glucose and other 

 nutrients were excluded and the saline and the cells were maintained at 4°C 

 during the experiment. The results shown in table 7 indicate that metabolic 

 incorporation of the labeled sulfate was small as compared to the quantity of 

 radiosulfate in the water space. From the loss of radioactivity of the immersion 

 fluid, the water space volume was calculated to be 84.7%. 



This is not the true water space since about 4% of the original radioactivity 

 in the medium was retained in the cells after washing. If this quantity is 

 deducted from the total cellular uptake, the water space corresponds to 75%. 

 The wash loss measurements give a water space of 72%. 



Permeability of Escherichia Coli to Phosphate Ions. Experiments carried 

 out on the permeability of E. coli to phosphate ions quickly revealed significant 

 differences between the responses of the cell to exogenous phosphate and to 

 sulfate ions. The metabolic incorporation of phosphorus by cells suspended in 

 sodium phosphate buffer is rapid, and it is consequently more difficult to dis- 



