146 



MICROSOMAL PARTICLES 



cally impotent protein, such would be the case. The linear rather than expo- 

 nential uptake in damaged cells tends to argue in favor of this hypothesis. We 

 intend to study specific cell fractions as a check. 



ACKNOWLEDGMENTS 



We wish to thank Stuart Hauser for assistance in the later stages, particularly 

 for the data for figure 5. Discussions with Ellis Kempner have been most 

 useful. 



SUMMARY 



The uptake of P 32 phosphate and S 35 sulfate and sulfide by E. coli as in- 

 fluenced by X rays has been studied. The initial uptake is not greatly changed 

 by doses up to 100,000 r, but the rate of uptake is radically changed at later 

 times. Expressing the ratio of the final rate of uptake to that of unirradiated 

 controls in terms of dose we find a logarithmic relation. Analysis in terms of 

 a sensitive volume gives large sensitivities as follows: 



Colony formation (for comparison) 



P0 4 uptake 



S0 4 uptake 



S uptake 



Methionine uptake (for comparison) 



4 X 10- 16 cc 



1.4 X10- 16 



9.5 xlO- 17 

 5xl0- 17 



io- 17 



The surprisingly large sensitivity for phosphate may mean that intact DNA 

 controls phosphorus uptake. The figures for sulfate, sulfide, and methionine 

 can be explained in terms of a synthetic chain of microsomal particles involv- 

 ing nine steps from S0 4 to protein and five from sulfide to protein. 



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