450 BACTERIAL PHOTOSYNTHESIS 



know what I mean when I say it's amazing what has happened after a 

 long dry spell of something like twenty years. All you have to do is 

 look at the literature in 1935, 1940, 1945, 1950, and so on, to see what 

 little was done back then, despite enormous efforts, and note what has 

 happened lately. 



Since we now have coupling enzymes and even active sites in the 

 mitochondria (which are incidently much more difficult systems to 

 work with than chromatophores, whatever they may be), I think it is 

 helpful to consider whether the sites in photophosphorylation have any 

 relation to the established sites in oxidative phosphorylation. Here I 

 think we must be guided by the concept of a certain unity in biochem- 

 istry and suppose there is probably a coenzyme Q— pardon me, a 

 ubiquinone— mediated site, a flavin mediated site, a pyridine nucleo- 

 tide mediated site, and a cytochrome mediated site possible. Now it 

 may be that the photosynthetic apparatus has short-circuited a few of 

 these, but it is still possible that Pinchot's work on bacteria will tell 

 us about one site, and the work on the cytochrome site in Green's 

 laboratory and in Boyer's laboratory will tell us about a second site. 

 Two sites is all we want right now apparently, so it will be fruitful to 

 operate on this assumption. As provided by Baltscheffsky, the data so 

 far for two sites in photophosphorylation are quite good, but not con- 

 vincing. 



Now having gotten over this, then, the picture one derives for the 

 photophosphorylation is that of an electron transport chain, in which 

 the usual oxidase is missing and which has the chlorophyll in a photo- 

 activated form as the oxidase. This idea is not new; it's quite old. I 

 don't know how far back it goes, but I know the first I heard of it was 

 from Hill, It doesn't make much sense of course, teleologically, for 

 an organism that is interested in throwing away oxygen to have an 

 oxidase; it doesn't make much sense for a strict anaerobe to have one 

 either, and yet both of them do in photosynthesis. So on this basis, one 

 would desire not to see an oxidase. It would create great difficulty 

 also, at least in my mind, to see how to avoid oxidation in chloroplasts 

 and chromatophores if there were an oxidase present. But there are 

 some difficulties about the chlorophyll as an oxidase on the basis of 

 potentials; I will speak of this a little bit later. Now to the cyclic and 

 noncyclic controversy. 



It seems to me this is a very much unneeded tempest. The question 

 of cyclic and noncyclic phosphorylation arises mostly out of the desire 

 to have a scheme which includes both the closed and open systems 

 which are possible in photosynthesis, and which can be manifested by 

 suitable experimental conditions. The crux of the matter is, what is 

 the stoichiometry? I don't think we went into this very much at this 

 meeting. If you have strict stoichiometry, then you have noncyclic 

 without any question, that is, if you can get nothing but 1.0 or 0.95 or 

 1.05 for the ATPiDPN ratios. It is obvious that such values are not 



