444 LIGHT AND LIFE 



insofar as the rccoiiihiiiation of the oxidized and reduced moieties is con- 

 cerned, we see in photosynthetic phosphor) lation a plK-nomenon very much 

 analogous to oxidative phosphoryhition. In otlier words, we see high energy 

 phosphate bonds made at the expense of energy released during electron 

 transport. There are, however, fundamental differences. In photosynthetic 

 phosphorylation, we do not use or do not consume an external hydrogen 

 donor, and we do not consume external oxygen. I will have more to say 

 about this this afternoon. So, in one case we have to pay for it very dearly 

 by providing a substrate for getting the energy and by providing oxygen. 

 In the other case, the only substrate which is being used is light. Light 

 makes both the oxidant and the photoreductant. For this reason, we intro- 

 duced the term photosynthetic phosphorylation to distinguish it from oxida- 

 tive phosphorylation while fully maintaining the concept of electron flow 

 between oxidized and reduced moieties. 



Dr. McElrov: I would say I need clarification on that because it seems 

 to me what you are saying is that you are merely using light energy to 

 create your substrate and your oxidant. That is the same as what Dr. 

 Lipmann just said. 



Dr. Arnon: I find it clarifying to think that light and cytochrome con- 

 stitute the oxidant in photosynthetic phosphorylation. This is what we 

 replace oxygen with. At the reducing end, we release an electron, which 

 instead of comi)ining with oxygen as it does in oxidative phosphorylation, 

 it recombines with chlorophyll via cofactors and cytochrome. I think it is 

 very important to keep in mind the distinction between oxidative and 

 photosynthetic phosphorylation. I do not think this is just a play on words. 

 It is rather important whether we consinne sugar or succinate or whether we 

 can get ATP without it. That is a rather fundamental point. 



Dr. Kamen: I was somewhat informally deputized to discuss Dr. Hill's 

 paper. However, before beginning my informal remarks, I wish to express 

 my feeling that these symposia are not places to rehash at length things 

 that are in the literature. They should be a forum for presentation of ideas, 

 whether half-baked or wholly baked, which are worthy of consideration even 

 though the work on which they should be based has not been done. Now 

 many of the ideas that you will hear about cytochrome function in phos- 

 phorylation are already in the literature. They are available and I don't 

 think we should take up our time with them unless there is something to 

 discuss in connection with them which is new. Otherwise, we will never 

 get to things which I think might also be interesting. Now, as I mention 

 in the paper I am sui)mitting, it is a privilege to appear as a discussant in 

 the first place following Dr. Hill inasmuch as it was an attempt to create his 

 reaction in iiacteria which led Dr. Vernon and me to our research some 10 

 years ago on cytochrome. I venture to say that the result of this has been a 

 remarkable numl)er of investigations. Unwittingly, we opened a Pandora's 

 box. Dr. Vernon and I a long time ago proposed that there would be back- 



