288 Raymond Latarjet 



in 4 days were considered normal. The percentage of normal 

 clones was inversely related to the number of mutations. 



The peroxide proved to be very toxic. Very few animals 

 survived exposure to 12 [xg./ml., but almost all survived 

 10 [xg./ml. Altogether, Dr. Kimball had 25 autogamous clones 

 from each of 344 treated animals of which 224 were exposed 

 to 10 [Jig. /ml. and 40 each to 12, 8, and 6 (Jig./ml. The percent- 

 age of normal exautogamous descendants from these 344 

 treated animals was 96-0, against 97-5 in the controls. The 

 difference is not significant. 



(b) Dr. Luzzati and M. R. Chevallier (1956, personal 

 communication), of Strasbourg, used resting Esch. coli strain 

 B. Full-grown bacteria in broth were washed and resuspended 

 in buffer in the presence of 1 X 10"^ to 2 X 10"* peroxide. 

 Contact was maintained during 30 minutes at 37°. The 

 survival ranged from 0-3 to 10-^. After contact, the bacteria 

 were washed and plated (1) for B/1 mutants, resistant to phage 

 Tl (end-point mutations); (2) for B/Sr mutants, resistant to 

 streptomycin. No induced B/1 mutant was ever observed, 

 whereas the treatment induced up to 4000 B/Sr mutants out 

 of 10^ survivors. 



This is one more example of mutagenic specificity (Demerec 

 and Cahn, 1953). 



Inactivation of pepsin by peroxide 



Most biological DNA is usually combined with protein. 

 We have seen that the hereditary material of bacteriophage is 

 very sensitive to peroxide, and it will be seen (p. 289) that pure 

 DNA of bacterial origin is even more sensitive. In order to 

 get some idea of what might happen to the protein moiety of 

 nucleoprotein treated with peroxide, a first series of tests has 

 been carried out on pepsin in this laboratory by Dr. Monier. 



CrystaUine Armour pepsin (P.M. 35,000) was dissolved, at a 

 concentration of 5 X 10-^ m in 0-1 M-acetate buffer. Succinic 

 peroxide was added, and after a certain time of contact was 

 removed by dilution. Proteolytic activity on casein was 



