454 BACTERIAL PHOTOSYNTHESIS 



oxidation. This has been shown ad nauseam in photochemistry and in 

 radiochemistry. You can get any product you want by manipulation of 

 the environment. 



Now the question is, what is the environment of the chlorophyll in 

 the photosynthetic apparatus? It is my contention that the proteins, or 

 the fats in which the chlorophyll is imbedded, are more likely to be 

 electron donors than electron acceptors. Most of the potentials one 

 finds in these organic substances are down in the negative reducing 

 region. Of course, there are double bonds around, which could be 

 acceptors, too. So some bright fellow has got to sit down and find out 

 what is the compound which sits next to chlorophyll, and in what kind 

 of an environment it is. This is the major problem in photosynthesis 

 today. If we could only know this much, then it would follow quite ob- 

 ligatorily what the reaction chemistry was, and that would help the 

 EPR people too. All we have heard today assures us that there is some 

 photochemistry, and that we have plenty of reactants for the chloro- 

 phyll to react with; which they may be depends entirely on what final 

 structural analysis shows. 



In the case of bacteriochlorophyll, there is a burning question of 

 what those bumps in the bacteriochlorophyll spectrum could mean. 

 Nothing like them is seen in the green plant chlorophyll, which ap- 

 parently differs from the bacteriochlorophyll only in that there are a 

 few minor changes in the hydrogenation level. There is a shift of over 

 a thousand angstroms, going from the native form to the monomer in 

 organic solvent. Moreover, as far as I know, nobody has been wholly 

 successful in reconstituting bacteriochlorophyll in its native form. 

 Thus, there is a question which has been left wide open as to what the 

 significance of these different absorption maxima are, in what is pre- 

 sumed to be a single tetrapyrrole structure. The very interesting 

 experiments of Newton on conformational changes evoked by variations 

 in ionic strengths may open avenues for elucidation of this problem. 



Well, I think I have tried to summarize— and to introduce, of course, 

 some propaganda of my own— on the status of bacterial photosynthesis. 

 I feel we know as much about it as we do about green plant photo- 

 synthesis, and this, I say chauvinistically, with much less effort put 

 into it in terms of man-hours, or woman-hours, than has been done 

 with green plant photosynthesis. I believe this is because Professor 

 van Niel, years ago. set the pattern with the comparative biochemical 

 approach. It brought into the field people who wouldn't ordinarily look 

 at an organism, as they wouldn't in the case of green plant photosyn- 

 thesis, which was supposed to be the domain of plant physiologists, 

 more or less! And besides, the bacteria have a much better biochem- 

 ical apparatus to play with, and are much more flexible. Even though 

 they maice no oxygen, which renders them no use whatever to mam- 

 mals, still the chances are we have found out more about photosyn- 

 thesis by study of bacterial systems. Most of the quantitative work on 



