SUMMARY 449 



specify more accurately the nature of the process in terms of which 

 we speak about a unitary theory. We have, I think, in bacterial photo- 

 synthesis, already a certain amount of information. It seems safe to 

 say that one process which unifies all photosynthesis is the photo- 

 oxidation of a c-type cytochrome. I haven't heard anything in these 

 last three days which seems to indicate that anybody has doubts about 

 this; of course, it is still a question for future research as to whether 

 the kinetics of these reactions accord with a primary process, but 

 they certainly do not have to accord with a primary process to be con- 

 sidered a feature of the unitary theory. Whether there is any other 

 reaction that is common to all photosynthesis or not, this is one that 

 certainly is. There is some question as to whether the splitting of 

 water might be considered common to all photosynthesis, but every- 

 thing that has been looked at so far does show an oxidation of cyto- 

 chrome. In the case of the splitting of water, the objection has been 

 you couldn't see it, you only could see the products. In the case of the 

 oxidation of cytochromes, you can see it in the test tube, in the spec- 

 troscope, and you can see it in vivo; so perhaps this is progress. 



Now the other thing that is important about this definition is the 

 fact that it leads to experiments, I hold, wholly out of prejudice, per- 

 haps, that the notion of a heme-protein magnesium tetrapyrrole com- 

 plex, which was first enunciated by Robin Hill, on the basis of com- 

 parative biochemistry and structure, is a fruitful hypothesis, however 

 true it may be. The work which has been done with flash spectro- 

 photometry by Witt and others, and with dynamic spectrophotometry 

 by Chance, Nishimura, Olson, and others, also indicates the possibility 

 of interpreting optical density changes in a rational, consistent way. 

 And these same studies dovetail beautifully with the sort of thing that 

 goes on in the kind of research which has been described by Vernon, 

 by Horio, and by others, on the enzymatic activities in photooxidation 

 and photoreduction processes of model systems. I don't think I have 

 to summarize these things further, but what I must do is get to the 

 vexing question of the terms cyclic and noncyclic. 



From the beginning it was my impression that there was only one 

 kind of phosphorylation, the esterification of the secondary phosphate 

 in ADP to ATP. What happened after could be specified in terms of 

 some reservation or qualification about the nature of the process 

 accompanying this phosphorylation. It seemed to help some people 

 to attach an appendix to the word phosphorylation— other than "photo," 

 that is. 



Now we should, I think, take our lead on these matters from the 

 people working in oxidative phosphorylation; it's not necessary, but it 

 may be helpful. They have been at it a much longer time than we have 

 and they have some possibility, apparently, of understanding this 

 process in the near future. Those of you who have followed the litera- 

 ture in oxidative phosphorylation in the last two years will probably 



