118 Discussion 



Alper: There is one point I would like to make. I don't know whether 

 our results at these extremely low oxygen concentrations are good 

 enough to be quite sure that we failed to demonstrate the effect I mean. 

 If you take the view that it is only after the respiratory chain is fully 

 oxidized that you get an oxygen effect, you should in fact have a little 

 tail to this curve. In the experiments on bacteria carried out by 

 Dr. HoUaender's group, quite a big tail is shown in the oxygen effect 

 curve. They worked with a closed system and a dense suspension of 

 bacteria so that they were able to use up the oxygen and did in fact 

 do so ; if the results are plotted out in this way you do get quite a tail 

 to that curve. We get the oxygen at these very low tensions by pro- 

 ducing it with an electrolysis cell and running the cell at currents from 

 10 mA upwards, so that we can get something of the order of 0-01 per 

 cent oxygen or less. You get a very slight but real increase at that 

 concentration, and increasing sensitivity as oxygen concentration 

 increases; there is some scatter in the points, but the results show this 

 clearly. 



/ Stapleton: Dr. Billen in our laboratory followed the respiration of 

 several strains of irradiated Esch. coli. He measured the consumption of 

 oxygen by these irradiated cells, and compared this oxygen uptake with 

 that of non-irradiated cells, using glucose as substrate. He found that 

 the control cells, of course, consumed oxygen at a constant rate with 

 time of incubation. Irradiated cells, on the other hand, although the 

 final population as measured by ability to reproduce themselves was 

 something like one viable cell in 10^, consumed oxygen at approximately 

 the control rate for a period of something like 40-50 minutes. Then 

 there was a reasonably sharp break in the curve followed by a slow 

 steady decay of the respiratory ability of the cells. I think what this 

 curve means is that all the cells are viable during this period of time. 

 The break may represent a change or a beginning of death of the 

 population. Billen did some further experiments to see if some correla- 

 tion could be made with ATP synthesis in the cells and found that under 

 the same conditions the irradiated cells can synthesize ATP at approxi- 

 mately the same rate as control cells. At about the same time that this 

 break in the oxygen uptake occurs, although the cells were making 

 ATP at approximately the normal rate, something like 80 per cent of 

 ATP synthesized by the cell was found outside rather than inside the 

 cell. This again could mean that the population is changing with respect 

 vto viability. 



Latarjet: We have material that could be of use to Dr. Laser. 

 Dr. Beljanski has treated several strains of Esch. coli with large amounts 

 of streptomycin on minimal medium, and finally isolated some stable 

 mutant strains which are unable to synthesize the porphyrin ring. They 

 are haemin minus and if you grow them on small amounts of peptone 

 you get bacteria which have none or at most 1 /500th the total porphyrins 

 of the normal strain. They have no catalase, no peroxidase, no cyto- 

 chrome, or at most very little. We were interested, not in the oxygen 

 effect, but in photorestoration. (Incidentally, these strains are as photo- 

 restorable as the wild ones.) But, hearing Dr. Laser, I wonder if such 



