106 LIGHT AND LIFE 



in fluorescence, sonic show an increase, and some are not influenced at all. 



Dr. Franc:k: Wliat did you say about migration of the excited state? 



Dr. Wkukr: In proteins which (ontain tyrosine alone, it is possible from 

 the polarization measurements to see the excited state migrate from one 

 tyrosine to another. 



Dr. Franck: But do you have any quantitative ways of measuring this? 



Dr. Wkijp:r: No, because the only calculations which can be made assume 

 a knowledge of the distance and orientation of the tyrosines in the molecule 

 and this is unknown. One can make calculations asstmiing that the tyrosines 

 are random, but this is certainly not true. 



Dr. Franck: Is the process by which it migrates the Foerster process? 



Dr. Weber: I think there is no doubt that it is the Foerster process. I 

 wanted to show an interesting example of the use of Foerster's theory by 

 using conjugates in studying protein properties. In these conjugates one can 

 show a transfer excitation from the tryptophan to an attached group, which 

 is an aminonaphthalene group. When you put the protein into urea the 

 relative distance between the two groups increases and the transfer becomes 

 very much weaker or entirely disappears. 



Dr. Franck: Did the proteins you used always contain a conjugated system 

 of double bonds? 



Dr. Wkber: Yes, I have not used any special kind of protein but I think 

 gelatin is the only one which does not have any aljsorbing tyrosine or 

 tryptophan although it does have some phenylalanine. 



Dr. Franck: Do they show no fluorescence? 



Dr. W'euer: They don't, except for impurities. Polylysine of course I have 

 used. 



Dr. Seliger: I have two questions. Dr. Porter said that he used methylene 

 blue and it was the triplet state of methylene blue which oxidized ferrous to 

 ferric. He proposed that it woidd stay in a solution from which all oxygen 

 had been removed. You, Dr. Weber, observed the same sort of thing and 

 supposedly your solution was not oxygen-free. 



Dr. Wkber: No, I was only attempting to photo-oxidize tryptophan to 

 excite it by oxygen. I did not care what the mechanism was. I was just 

 measuring tryptophan disappearance. 



Dr. Seliger: So you were not postulating the same mechanism. That is, 

 that the triplet state is doing the oxidation. 



Dr. Weber: No, I was postulating nothing. 



Dr. Seliger: Just one more question. Ciould you say something very briefly 

 about tlie method used to obtain (juantum yields and then could you 

 postulate some mechanism whereby you coidd explain the decrease in 

 quantum yields with change in wavelength. 



Dr. Weber: The method I used to measure (]uantinn yields was published 

 in the Tidnsnctions of the Faradny Society in 1957. It consists in the com- 

 parison of the emission with a solution of glycogen in which the glycogen 

 scatters light and sets a quantum yield standard of one, correcting for the 



