56 E. F. MACNICHOL, JR. 



luciferin consumption. You can also show the same thing with ATP now, an 

 observation we couldn't make before. But it means you have to go to very low 

 ATP levels to show this quantitatively. Actually, it takes very little of this 

 material to give a bright light. Energetically, this is a very sensitive system 

 because you do not use very much material to get the energy for light produc- 

 tion. 



Dr. Morales: You mean that both are used up? 



Dr. McElroy: Yes. 



Dr. Morales: Then how do you have any ideas as to which is which? 



Dr. McElroy: You mean in terms of the energy source? 



Dr. Morales: Yes. 



Dr. McElroy: Well, we need 70 kilo calories. This is getting into the mech- 

 anism of luminescence and I am sure that that has nothing to contribute to 

 receptors. But I would just make one comment. 



Chairman Gerard: This is a typical transducer problem. 



Dr. McElroy: Yes. We need 70 kilo calories for the peak light. The reac- 

 tion between ATP and LH-2 leads to the formation of an active molecule which 

 can be oxidized. We know this molecule is oxidized. It is not oxidized in the 

 absence of ATP. ATP in some way brings about an activation for this oxida- 

 tion. It is very doubtful that a straight oxidation of this type of molecule could 

 give enough energy. So we feel that an organic peroxide is formed with one 

 such active molecule and this, in turn, leads to a peroxidation of a second mole- 

 cule. From such a peroxidation one can get roughly 70 kilo calories. We know 

 that luciferin is the emitting molecule because it has a fluorescent spectrum 

 which is identical to the chemiluminescent spectrum and that this changes with 

 pH. So this particular molecule is the one that becomes excited and the energy 

 in this case, you might say comes not from ATP but primarily from an 

 oxidation. One might say ATP contributes activation energy and the main 

 energy for subsequent excitation comes from the peroxidation of the luciferin 

 molecule. 



Dr. MacNichol: I am very much struck by what Dr. McElroy has to say. 

 I mean, here is apparently just the inverse of the photochemical reaction. Wald 

 has shown that the condensation of protein, in the case of the eye, is an energy 

 yielding reaction, so much energy is required and light energy gives a sufficient 

 amount to split these apart. Now here you have these two active compounds, 

 which combine in an energy yielding reaction and produce light. Is there any- 

 thing in your system which would show where we go from there? 



Dr. McElroy: I look at that as exactly the same as this. One has to, I 

 think, in energy reaction distinguish between that and activation energy. If 

 you have two molecules bound together, A and B, and you want them to go 

 over to A plus B with the energies given out — if I understand the situation 



