84 



ERNEST POLLARD 



on lactose,, no effect of radiation up to 75,000 r could be seen up to 

 45 mill after irradiation. To make the enzyme assay it is necessary to 

 open the cells. The method used was rapid expansion under pressure 

 and Avhile the recovery of enzyme was always good the data scatter 

 more than for the radioactive uptake experiment. Nevertheless there 

 is no reason to suppose that the immediate effect of ionizing radiation 

 on enzyme formation differs greatly in sensitivity from that observed 

 for amino acid incorporation. At later times after irradiation the story 

 is quite different. A dose as low as 15,000 r quite clearly gives a reduced 

 yield of enzyme. Data for different doses and different times are shown 

 in Fig. 5. It is quite clear that a process which involves the develop- 

 ment of the cell is at work. A clear decision as to the nature of this 

 process cannot, at the moment, be made. 



RADIATION ACTION ON THE PROCESS OF INDUCTION 



For this particular enzyme it is necessary that cells which have 

 grown on glucose become adapted, or induced, before they are able to 

 make the enzyme if they are grown on lactose. The above described 

 procedure can be applied to cells which have not been induced and 

 radiation action on the process of induction can be studied. A typical 

 time sequence is shown in Fig. 6. The first clear reading of the enzyme 



_o 

 o 



cr 



21,000 r 



Control 

 turbidity 



Control 

 enzyme 



Irr. 

 turbidity 



enzyme 



160 



Time (min) 



Fig. fi. — The effect of 21.000 r on the larocess of induction of ^-galactosidase. The effect 



on turbidity is shown for comparison. 



in the control appeared at about 60 min and thereafter rose sharply 

 and steadily. The irradiated cells also showed a small reading at 80 min 

 which corresponds to the same as the control, but thereafter rose much 



