CARBON MONOXIDE INHIBITORS 325 



association with that particular chlorophjll molecule, it still would have a good 

 chance to be involved in the photochemistry. 



Second, I want to ask Dr. Arnon whether he has any evidence of any CO effect 

 with chloroplasts. 



Arnon : We have not tried any carbon monoxide effects with chloroplasts. We 

 have a system in which chloroplasts under anaerobic conditions generate ATI' at 

 the expense of light energy, but do nothing in the dark. The chloroplast system 

 forms ATP, and reduces COj to sugar. Thus, insofar as photosynthesis by chloro- 

 plasts is concerned, we reach the conclusion that it is independent of oxygen. 



Krall : But it does this only in the presence of ascorbic acid and riboflavine? 



Arnon: Phosphorylation is done also in the presence of menadione or other 

 vitamin K substances. Incidentally, chloroplast is the only natural source of vita- 

 min Ki, and that is the reason we have been looking for a function for vitamin K, 

 Ascorbic acid has also been associated with chloroplasts. There is extensive litera- 

 ture on this subject, going back many years to the Molisch reaction. Flavin is also 

 present in chloroplasts in large amounts. So in answering your question, I am add- 

 ing the implication that these cofactors are not extraneous substances and that we 

 are observing no artifacts but effects which presumably play a part in these re- 

 actions in vivo. 



Krall: Wlien you first isolated your photosynthetic phosphorylation reaction 

 didn't you show an oxygen requirement before you added these things? 



Arnon : Yes, that is so, but that was before we knew about the cofactors. 



Rabinowitch: With regard to Dr. Granick's suggestion as to whether a weak 

 band can be used in the transfer of energy from one pigment to another, the an- 

 swer is that the probability of transfer is proportional to the probability of transi- 

 tion. If the transition is extremely weak, the transition is of a different t>'pe, it is a 

 vibrational transition; or if the transition is micronic, that is, a very weak band, 

 the probability of transfer is correspondingly low. It goes to zero when the inten- 

 sity goes to zero and the state is nonexistent. 



Then to answer Dr. Strehler's remarks, of course, you can use light quantities 

 absorbed by chlorophyll molecules in order to produce final transformations in 

 nonchlorophyll molecules. After all, that is what photosynthesis is about. So there 

 is no doubt, for example, that you could use energy absorbed by chlorophyll in 

 order to do something to cytochromes, but not by the resonance energy transfer 

 mechanism. 



Strehler : I thought that was what Dr. Kamen meant when he made that state- 

 ment. 



Rabinowitch: Nobody has any objection to saying that instead of reducing 

 carbon dioxide it reduces cytochrome /. One is as possible as the other. 



[See also Discussion following paper by M. D. Kamen, p. 162.] 



References 



1. Hill, R., and WTiittingham, C. P., "The induction phase of photosynthesis in 



Chlorella determined by a spectroscopic method," New Phytologist, 52, 133 

 (1953). 



2. Krall, A. R., and Burris, R. H., "Evidence for the participation of cytochrome 



