109 



KAMEN: The important point here is that there is an efficiency for energy 

 transfer which corresponds with what you would expect in synthesized fluores- 

 cence. That is the important point. 



KASHA: May I make one more remark. At a recent conference, another 

 very important observation was made: That was that the reversible bleaching 

 of chlorophyll A in the absence of air, or oxygen especially, persisted for 10" 4 

 seconds roughly. This is what Livingston reported. The significance is that 

 although no one has ever found a long-lived chlorophyll, he has indirect evidence 

 for it for the first time. 



TOBIAS: It seems to me that the system studied by Duysens might be a 

 very good one to test these mechanisms proposed yesterday for X rays, gamma 

 rays, etc. I think what you would find would be that the photochemical efficiency 

 there would be very low. 



BURTON: When you were talking about liver and enzymes you pointed out 

 that very frequently our difficulty is that we observe not the immediate effect 

 but the much later observable biological effect. As Dr. Pollard pointed out, 

 this fact is itself evidence of the great sensitivity of the biological system. This 

 is not an unusual thing in chemistry. After all, it is a very frequent thing. You 

 know that in kinetics we frequently observe not the primary effect but a very 

 much greater effect, for example, the result of a chain reaction. We all know 

 this, and lately we have been able to make inroads on the immediate effect by 

 tracer technics, for example, to discover the radical which started the affair. 

 Williams et al (8) have been doing such work with radioiodine, thus detecting 

 the first radical produced. 



Dainton (9) did similar work, producing polymers and determining what 

 radical added in. This is a very cute technique. It is the type of cute technique 

 that chemists have been using very successfully to find out something about 

 this first step. The only reason I mentioned this right now is because the biolo- 

 gists (I don't want to appear critical and this is not intended to be that way) per- 

 haps have been lazy in the way that chemists have been lazy. It has been so 

 easy to observe the big effect they have not given much thought to going back 

 and seeing whether there is any chance of observing the primary event, whether 

 there might not be techniques by which they may be examined. 



POLLARD: Biologists have been seeking the primary effect for a long time. 

 It is well known from the work of Beadle and Tatum (lu) that enzymes are pro- 

 duced by genetic action of some kind. What the radiobiologist is seeking is the 

 radiation mechanism involving the thing that forms the enzymes. What you have 

 to look for is not the effect on the enzymes but on the thing that makes the en- 

 zyme. 



BURTON: But in this particular instance, Dr. Kamen told us of a case 

 where the isolated enzyme would have a tremendous effect. The point is, is the 

 liver shielding the enzyme or reproducing it? 



MAZIA: The experimental problem is to measure the actual turnover of en- 

 zymes. This is something that the biological chemists would very much like to 

 do quite apart from the problems that we are discussing. It is still too diffi- 

 cult. The difficulty arises from the fact that we don't generally have methods 

 for quantitative assay of enzymes in the analytical chemist's sense of the term. 

 We have to use arbitrary measurements based on catalytic activity. 



KAMEN: I think we should avoid getting into questions of biological mech- 



