282 



H. CHANTRENNE 



restoration becomes more and more sluggish as guanosine is added later 

 and later. Moreover, qualititative changes are observed among the protein 

 produced during restoration. 



Figure i{a) shows how the synthesis of protein material — as measured 

 by phenylalanine incorporation — is restored when guanosine is added 30, 

 45 and 60 min. after azaguanine. In the same experiment, the synthesis of 



750 



500 



250 



30 



45 



180 

 (min) 



(a) 



360 



180 

 (mm) 



(b) 



360 



Fig. I. Restoration of protein and penicillinase synthesis [7]. To five growing 

 suspensions of B. cereus (penicillinase-constitutive mutant) containing 008 ^C 

 of L-['*C]-phenylalanine per ml., 36 /xg. of 8-azaguanine were added at time o. 

 Guanosine (135 /xg./ml.) was added respectively o, 30, 45 and 60 min. after 

 azaguanine. No guanosine was added to the last suspension (00). 



(a) : '""C in protein material (c.p.m. per ml. suspension). 



(6) : penicillinase (units of activity per ml. suspension). 



constitutive penicillinase — as measured by its enzymic activity — was 

 determined; the results are shown in Fig. i(b). Comparison of figures i{a) 

 and i{b) indicates that when guanosine is added 45 or 60 min. after 

 azaguanine, penicillinase production is still completely obliterated at a 

 time when the synthesis of protein material was already restored to a 

 considerable extent [7]. 



The damage caused by 8-azaguanine to the formation of the enzyme 

 penicillinase is therefore more severe or more difficult to repair than the 

 damage caused to the synthesis of protein material as a whole. Moreover, 

 it becomes worse and worse as the time of action of azaguanine increases. 

 All the enzymes, however, do not suffer as much as penicillinase. For 



