lO ELECTROLYTES IN BIOLOGICAL SYSTEMS 



acetic acid soluble fraction of the cells. In addition to this metabolic uptake, 

 further incorporation is observed when the cells grow. This later uptake (into 

 the TCA precipitable fraction) corresponds to protein synthesis and is pro- 

 portional to the quantity of new cells grown. 



Fig. 3. Radiosulfate uptake by T. iitilis. Curve A represents radioactivity of TC.\ soluble 

 fraction observed during the growth of the cells, shown by Curve B. The ratio A/B indicates 

 that no fixed quantity of sulfur is maintained in this fraction during growth. 



Figures 3 and 4 show these relations. A comparison of immediate uptake of 

 sulfur in T. utilis and in E. coli cells is shown in table 6. In this experiment 

 approximately equal quantities of washed T. utilis and E. coli cells were sus- 

 pended in 2 ml of glucose-free, chilled synthetic medium containing radio- 

 sulfate. The immediate sulfate uptake by each type of cell is indicated by the 

 loss of radioactivity in the supernatant fluid. E. coli removed a total of 16% 

 of the original radioactivity which corresponds to a water space of 75%. 



