14 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



On the other hand, the residual radioactivity remaining in the cells after 

 washing indicated that some metabolic incorporation had occurred during 

 the brief immersion of the cells in the chilled buffer solution. This metabolic 

 uptake is dependent on the length of time of immersion of the cells in the 

 radiophosphate medium, and on temperature. In a parallel experiment in 

 which the cells were maintained at 37°C for 40 minutes, this metabolic binding 

 becomes much more evident. Table 8B shows that under these conditions the 

 washing fluid contains, in addition to the water space P^-, a quantity of phos- 

 phorus equal to approximately 20% of the bound phosphorus. In the imme- 

 diate uptake experiment (table 8A) the presence of proportionate quantities 

 of 'loosely bound' phosphorus would not markedly alter the water space 

 volume determined. The radioactivity in the cells is found to be independent 

 of the phosphate concentration but does depend on the presence of the ammo- 

 nium ions, a fact which indicates some metabolic incorporation. 



Table 9. Distribution or P^ in e. coli 



Fractionation of the cells containing phosphorus taken up during a brief 

 immersion in a cold radioactive medium shows that this phosphorus is largely 

 inorganic. The results of such a fractionation are shown in table 9. The dis- 

 tribution of P'^ in cells which had 40 minutes' growth at 37°C in the same 

 medium is shown for comparison. 



Permeability of Escherichia CoJi to Glucose- 1-Phosphate and Fructose- 

 1 : 6-Diphosphate. The permeability of these cells to I"--labeled glucose- 1 -phos- 

 phate has also been measured. The radioactive compound was prepared by a 

 method described by Umbreit, Burris and Stauffer (29). A suspension of 

 approximately i ml of cells in 5 ml synthetic medium was chilled to 4°C and 

 added to 5 ml of the radioactive glucose- 1 -phosphate solution (0.8 mg P/ml). 

 For comparison, an equal quantity of chilled, suspended cells was added to 

 5 ml of a mixture of 5.5 ml synthetic medium, i ml of 5% glucose and carrier- 

 free P^-. The cells were immediately centrifuged, rinsed and washed with 0.85% 

 NaCl. Aliquots of the cells and washing fluid were measured for radioactivity. 

 The results, shown in table 10, indicate that the uptake and wash loss were 

 equal to those observed for phosphate ions. No exclusion of the larger mole- 

 cules is observed. 



