298 Discussion 



Spiegelman : So you really have a heterogeneous population with 

 respect to the sensitivity to attachment. 



Latarjet: I wouldn't say attachment. 



Spiegelman: That's just an analogy. 



Alper: Whether or not radical reactions in the classical sense could 

 take part in events inside the cell, it seems that there is something 

 rather mysterious going on in the radiation chemistry of various in vitro 

 systems. Dr. Dale has told us that all the enzymes that he has investi- 

 gated in dilute solution showed no oxygen effect. This seems all right if 

 the changes are due to — OH radicals, because the presence of oxygen 

 does not affect the number of these radicals. Whether any of these 

 systems have also been examined in the presence of hydrogen, I don't 

 know; but certainly it does seem rather inysterious in Dr. Latarjet's 

 case because he has tried oxygen and he has also tried hydrogen. Now 

 if you are going to regard the agent responsible as the — OH radical 

 (and I should think on any sort of radiation chemical picture we must 

 still regard indirect action in in vitro systems as due to radicals), it is very 

 difficult to see how you can get indirect action which is not affected by 

 the hydrogen, which converts — OH radicals into hydrogen radicals. 



Latarjet: May I say that perhaps we have an artifact in the experi- 

 ment carried out in the presence and in the absence of hydrogen, since 

 the material was very radiation-resistant. We worked with doses of up 

 to 500,000 r and, in the absence of gas, we did not prevent the formation 

 of a great amount of hydrogen radicals in the medium due to radiation. 

 Therefore, there was perhaps in this instance no experiment at all in the 

 absence of hydrogen; all were probably in the presence of hydrogen. 

 That might account for the fact that we did not find any difference with 

 and without hydrogen. 



Alper: This means that your in vitro indirect effect could be due to 

 hydrogen radicals, and this is the only thing it could be that would fit 

 with your experiments. 



Alexander: I don't think that interpretation is necessarily valid, if we 

 accept some of Dainton's latest work that the reaction between hydrogen 

 and — OH radicals to give H atoms is not very favourable. If there is 

 nothing else for the — OH to react with then this reaction will occur, 

 but in Latarjet's system where there are great quantities of proteins 

 and other organic matter, it is most unlikely that the — OH radicals will 

 interact with dissolved hydrogen. We found that as little as 0-02 per 

 cent of organic matter prevented the reaction of hydrogen at atmospheric 

 pressure with H atoms (Alexander, P., and Fox, M. (1954), Trans. 

 Faraday Sac, 50, 605). 



Latarjet: Our preparation was highly active; we had one million 

 transforming units per [ig. of DNA. That is a great advantage and 

 therefore we worked with an amount of DNA whch was about 10" ^ [ig. 

 per g. 



Spiegelman: But it was protected. 



Latarjet: It was very much protected by 10 per cent yeast extract. 



Alper: This means that the hydrogen cannot react with the — OH 

 because there is a lot of organic material present to grab the — OH. But 



