DISCUSSION 417 



dition of the chloroplasts. It is very hard to <>ct good yields with poor 

 cliloroplasts. Do vou sec any possible relation between the condition of your 

 chloroplasts and the yields which you obtained? 



Dr. Kok: No. For phosphorylation measurements all the care that you 

 described in your papers for treating the leaves was taken. The quantum 

 yields always come out very, very low (~ 0.02) . Have you measured it? 



Dr. .\rxon: We have nothing to report on quantum yields at this time. But 

 I would like to ask another question. I am not quite clear what you are 

 measuring with PMS. Do you measure photophosphorylation? Spectral 

 changes? Have you compared phenazine methosulfate with other catalysts 

 for photophosphorylation and were there any differences? 



Dr. Kok: I want to emphasi/c the fact that PMS is the only oiie and very 

 typically the only one that will stimulate the light-induced bleaching of P700 

 in cell-free preparations. FMN, dye, whatever you use, and there are a 

 number of others, always tend to have the opposite effect on our pigment 

 system. They do not act like PMS at all. 



Dr. }agendorf: I am surprised that you call PMS a reducing agent. It 

 should be oxidized when you add it unless you have ascorbate there also. 



Dr. Kok: I do not know what it means, but it stimulated the shift reduced 

 dye no matter how you put it in, as pyocyanine or as PMS. We tried all 

 sorts of things and it seems to establish itself in illuminated chloroplasts. 



Dr. Lipmann: If you have a chloroplast to which you give some substrate, 

 you get a reduction of PMS. But one cannot call PMS a reducing agent 

 because it gets reduced. 



Dr. Kok: That's right, but we can produce the same effect with reducing 

 agents like ferrocyanide or molecular or atomic hydrogen. This similarity 

 of action makes us think that PMS carries out a reducing step some way or 

 other. 



Dr. Calvin: I just wanted to add a remark at the end of the talk earlier 

 today. I just didn't get a chance to. The wavelength for maximum quantum 

 yield of spins is around 715 m/t for chloroplasts. 



Dr. CoM\ro\ER: It seems to me that in the absence of a fully resolved EST 

 signal (which is the case in Dr. Calvin's results) quantitative estimates of 

 spin numbers should be treated with considerable caution. 



Dr. Calvin: I said the wavelength for maximum of the total number of 

 unpaired spins produced in chloroplasts is 715 m/x, the total number of spins. 

 They are unpaired electrons. 



Dr. Rabinowitch: I'd like to ask Dr. Kok how it is from his point of view 

 that monochromatic light absorbed entirely by phycoerythrin can give com- 

 plete photosynthesis with a high yield. 



Dr. Kok: If you look at the spectrum for acti\ation of the positive return 

 step in chloroplasts, it looks exactly like enhancement activation. It has a 

 shoulder at 670 m/i, a peak at 650 m^u (and then it gets lost in the blue. 

 Something strange is going on there) . This means that the plus shift does 



