108 



ZIRKLE: That is due to deficient observation, I am sure. 



KAMEN: The difficulty is you cannot think how to find out what happens in 

 the very first micro-seconds. 



ZIRKLE: There are no suitable techniques. 



POLLARD: The other thing is to say that biological observation is extreme- 

 ly sensitive and you have to wait for the biological amplifier to take effect before 

 you can detect. The mere fact that the biological system reproduces something 

 many times later gives a tremendous sensitivity. 



KAMEN: This situation is no different from that encountered in many kine- 

 tic studies where the primary reactions are so fast there is no hope of freezing 

 them. Nobody has ever particularly worried about this. What you look for, 

 therefore, in biological systems is something which you can relate to a model 

 outside. One of the most notable cases, of course, is the case of the coopera- 

 tion between pigments in photosynthesis. In the case of photosynthesis, it is 

 known that there is an association of pigments, including various chlorophylls. 

 Usually chlorophyll A is predominant. There are also carotenoids and other 

 pigments, perhaps some in trace concentrations we don't know the existence of. 

 In any case, the one pigment in the green plant which has the lowest ground 

 state, that is, the longest wavelength for fluorescence, is chlorophyll A. 

 Everything else has a shorter wavelength fluorescence including chlorophyll B. 

 It turns out, and this is what you would expect according to what Dr. Linschitz 

 has told us, that all the energy funneled in anywhere along the line finishes up 

 in chlorophyll A. It is a major triumph for the radiation theory in that it pre- 

 dicts this result with regard to the functioning of the biological system. A com- 

 plete job has been done by Duysens (7) on this. Also it is true in the case of 

 bacteria where you have bacteriochlorophyll, which is not very well character- 

 ized in the organism. If you extract it you can characterize it, but all you get 

 is one substance. In the organism, the absorption spectrum associated with 

 this dye is rather complex, showing many peaks in the infrared around 870 m \i , 

 910 m [i , and so on. The extracted pigment has only one big, broad absorption 

 displaced from the infrared toward the blue. The point is that you can send in 

 light at any of these frequencies and yet the only frequency that is usable in 

 bacterial photosynthesis, is the one that corresponds to 910 my. , the longest 

 wavelength. In every case the energy degrades itself to the lowest lying stable 

 state available. 



All this is only to amplify Dr. Linschitz 's talk. 



FANO: Who has found out all these things? 



KAMEN: These are experiments by Duysens (7). 



KASHA: I should like to make a correction in your statement. What Duysens 

 observed is not exactly what you said but very close to it. A slight correction, 

 if I may. He did observe that the only emission in those systems with many 

 dyes present was from the lowest fluorescent state of chlorophyll A. However, 

 we don't know whether that emission corresponds to the energy available for the 

 photosynthetic act or whether the complementary part of the quantum efficiency 

 not observed is responsible for the photosynthesis act. In other words, the 

 quantum yield of that fluorescence is not 1; it is lower than 1. We don't know 

 whether the 0.4 of a quantum efficiency observed is responsible for the photo- 

 synthesis or whether it is the 0.6 not observed that is responsible. 



