RADIATION AND THE CELLULAR SYNTHESIS OF PROTEIN 85 



less definitely and a])])eared to flatten somewhat between 140 and 

 240 niin. even though the culture was showing an increased turbidity. 

 After 4 hr there is an increase in enzyme, but we also noticed some 

 enz3^me leaking from the irradiated cells into the medium, a feature 

 not observed in the controls. 



Increasing the dose had the effect of depressing the development of 

 enzyme into the region hard to measure. After 320 min, a culture which 

 had received (30,000 r barely gave a readable amount, although small 

 readings had been recorded when the control began to show the presence 

 of enzyme. The data are summarized to some extent in Table IV. The 

 ratio of enzyme for irradiated cells to control cells is shown for various 

 times. It was also observed that the amomit of enzyme, for both control 

 and irradiated cells approximately follows the development of turbidity. 



It is once again clear that a process involving cellular development 

 is involved. 



Table IV 



Dose Ratio of enzyme to control at intervals after induction 



(r) Omin 30 min 90 min 180 min 



UPTAKE OF 35S AS SULPHATE 



Radioactive sulphate is primarily incorporated as protein. A general 

 idea of protein synthesis can be therefore obtained from an observation 

 of sulphate uptake after irradiation. It w^as found that very little effect 

 was observed on the ability of the cell to incorporate sulphate for times 

 up to 12 min unless doses over 200,000 r were used. A rough estimate 

 of the 37 per cent survival dose is 300,000 r. The immediate effect of 

 radiation is thus very much like the effect on the uptake of amino acids 

 and so is probably due to the disruption of ribosomes in some way. If 

 longer times of uptake are considered there is a marked effect as can be 

 seen from Fig. 7. The uptake follows the normal and then, rather 

 sharply, deviates from the exponential line and becomes linear, in- 

 creasing at lower rates w ith higher dose. The aj)pearance is rather like 

 the production of enzyme and confirms the general behaviour seen there. 

 Some secondary development process is again taking place. The irradi- 

 ations described were under conditions which were nearly anaerobic. 

 If oxygen was bubbled, a given dose had definitely more effect, both in 



