124 B. L. STREHLER 



metastable states — a partly self-perpetuating reaction which involves no chem- 

 istry. 



Strehler: That is certainly a possibility. The only thing about trying to deter- 

 mine the rate of back reaction is that one has to assimie that the fluorescent yield 

 from all chlorophyll molecules is identical. It may be that the very molecules that 

 are involved in the photochemistry have a much different quantum yield for 

 fluorescence than do the average — higher or lower. 



Rabinowitch: Still, did 3'ou ever look whether red phosphorescence occurs in 

 chlorophyll solutions? 



Strehler: We have never been able to detect with the quantum counter a 

 luminescence of chlorophyll in anaerobic solutions after illumination. There is a 

 chemiluminescence of chlorophyll in solution which I will mention, verj' briefly, 

 later in this session. This luminescence does have a longer lifetime but is probably 

 only of interest from a chemical standpoint. 



Weigl: If the reactions of this primary product are enzymatic, as they almost 

 surely must be, it ought to be possible somehow to find a specific inhibitor for one 

 or another of the steps and to increase the luminescence by adding inhibitors. 

 Have you had any luck with that? 



Strehler: Cyanide, azide, phenylurethane — a variety of substances increase the 

 limiinescence up to almost twofold before they begin to inhibit. We have made the 

 argument earlier that this is consistent with the idea of the pile-up of intermedi- 

 ates. Hydroxylamine has a specificity of action which most of the other inhibitors 

 do not have, in that it seems .selectively to depress the long-lived luminescence 

 but to inhibit the short-lived luminescence to a much lesser e.xtent. 



Gaffron : I remember that at least in the first experiment with hydro.xylamine 

 N'our concentrations were rather high. Do you have one in the physiological range? 



Strehler : Yes, hydroxylamine is effective at around 10^^ mole in intact Chlorella 

 for inhibiting the long luminescence. 



Frank Allen : What is the possibility that this luminescence might be coupled 

 with the decomposition of peroxide? 



Strehler: I think that the primary oxidant might be something perhaps analo- 

 gous to a peroxide. One just can't answer your question until one has the system 

 in extract. 



James Smith: If the luminescence spectrum is the same as the fluorescence 

 spectrum of chlorophyll, doesn't this practically eliminate the need to look for a 

 pigment that absorbs at longer wavelengths than chlorophyll in the radiation 

 transfer? 



Strehler : Except for antistokes sensitization. 



James Smith : It seems to me that, if the reaction products react and re-activate 

 the chlorophjdl, it must be the end of the line so far as the radiation transfer is 

 concerned. 



Strehler : I think that is a good argument. What do you think, Dr. Arnold? 



Arnold : I have thought about it. I am not sure that a triplet state of chlorophyll 

 is not produced by the back reaction, and that the triplet crosses over into an 

 excited singlet which emits the luminescence. 



James Smith: If a pigment other than chlorophyll were e.xcited in the back 

 reaction, wouldn't you get a luminescence of this pigment? 



