POLLARD AND KENNEDY 



145 



METH 



sq,gso 3 



<\aCT. METH S0 3 



— "—J METHIONINE 



R 2 SH 



R 2 SH^ 



v^r.sh 





s 2 o 3 



so 



e? 



' f X ' 



;V > ^> 



\ 



\ 



Fig. 7. A schematic diagram to indicate the reason for the high sensitivity of sulfate 

 uptake. A series of reduction and combination steps, requiring enzymes (indicated as 

 rectangles), has to be complete before the activated amino acid can be incorporated. Each 

 enzyme is made by a microsomal particle vulnerable to radiation. Hence the sensitivity for 

 a nine-step process is nine times higher than for a single step. 



medium is a real effect. Otherwise the major conclusion is that no change in 

 the broad distribution is observed. 



That the initial uptake is unchanged, but reduced uptake occurs sooner 

 for more heavily irradiated cells, argues that a considerable amount of incor- 

 poration can go with the damaged synthetic apparatus, but that an unbalance 

 occurs as the cell develops. If the damaged ribosomes were making enzymati- 



TABLE 2. Cell Fractionation under Various Conditions 



Fraction 



Alcohol-soluble (lipids, protein) 



Cold-TCA-soluble (transient inter- 

 mediates, glutathione) 



Hot-TCA-soluble (nucleic acid 

 hydrolysates) 



Residue (protein) 



