58 



with 60,000 r. The respiration experiments that Dr. Sherman has discussed 

 were designed for the purpose of finding the energy source for this repair, and, 

 as he has shown, the total oxygen consumption is considerably higher at subopti- 

 mal temperatures than at 37°C. The nutrient necessary for this recovery proc- 

 ess can be obtained from yeast, beef or spleen extracts. A synthetic medium 

 consisting of inorganic salts, glucose, glutam.ate, uracil, and guanine is also ef- 

 fective. 



Although it is possible to omit some of the constituents of our synthetic 

 medium and still produce a few pinpoint colonies. This is not a reliable method 

 for studying the recovery phenomenon. 



The basis for these experiments is the feeling that cell division places 

 a great demand on the available enzymes and nutrients. If the cell is not able to 

 synthesize these quickly enough, it will die. The process of cell division is ex- 

 tremely slow at 18°C. After the repair process has taken place at 1 S^C , the cell 

 can be warmed to 37°C and many of the cells that have been damaged by radia- 

 tion will recover and grow quite normally. 



POTTER: Is your synthetic medium rich in certain nucleotide pre- 

 cursors? 



HOLLAENDER: Yes. Actually the synthetic medium was better than 

 yeast extract in restoring ability to form new colonies. 



POTTER: Have you ever examined the fluid that these cells are in, 

 from the standpoint of UV substances? That sort of thing has been done many 

 times, but is there a correlation in this case? 



HOLLAENDER: Very little ultraviolet absorbing material will diffuse 

 from X irradiated cells kept in salt solution. However, if the cells are given 

 some glucose, the ATP as well as other substances absorbing at 2600 ^ will dif- 

 fuse out quite readily. (IZ) 



POTTER: I think that is highly relevant. 



SHERMAN: I wonder if acid soluble nucleotides are decreased in ir- 

 radiated cells because of leakage. 



HOLLAENDER: We do not have quantitative data yet in regard to the 

 leakage problem. 



POTTER: If isolated rat liver mitochondria are suspended in isotonic 

 sucrose, there is no leakage of nucleotides from the mitochondria at 0*-' in the 

 presence or absence of substrate. When the temperature is raised to 30°C, 

 there is a progressive leakage of nucleotides from the mitochondria in the ab- 

 sence of substrate. However, this is not the case when substrate for mitochondrial 

 respiration is present. I think that this would provide an excellent and reproduc- 

 ible test system for study of effects of irradiation. 



SHERMAN: Can you get enough mitochondria to do some sort of frac- 

 tionation? 



POTTER: Yes, readily, and you can get the complete profile of the 

 nucleotides. They contain 25 or 30 different nucleotides. 



CARTER: In a supplement of the British Journal of Radiology, there 



