RELATIONSHIP BETWEKN REDUCINC FACTOR AND REDUCTASE 453 



References 



1. Hill, R., Proc. roy. Soc. B. 127, 192 (1939). 



2. Davenport, H. E., Hill, R., and Whatley, F. R., Pruc. roy. S(jc. B. 139, 346 

 (1952). 



3. Davenport, H. E., and Hill, R., Bwclu'm.'J. 74, 493 (i960). 



4. Hill, R., Northcote, D. H., and Davenport, H. E., Nature, Loml. 172, 948 



(1953)- 



5. San Pietro, A., and Lang, H. AI.,;7. biol. Chem. 231, 21 1 (1958). 



6. Davenport, H. E., Biochem.J. 77, 471 (i960). 



7. Arnon, D. I., Whatley, F. R., and Allen, M. R., Biuclum. hiuphys. Acta 32, 47 



(1959)- 



8. Jagendorf, A. T., Fed. Proc. 18, 974 (1959). 



Discussion 



Jagendorf: I should like to mention here that essentially parallel researches 

 are going on at Baltimore, by Dr. San Pietro and associates. If he were here, he 

 could have been given almost the identical paper from his own data. The identities 

 extend to the requirement for higher levels of the reductase enzyme, a three-fold 

 stimulation of the rate of TPN reduction when the complete phosphorylating 

 system is added, and a response to uncouplers. 



Arnon: I would like to make one brief comment and to ask one question. I 

 think it is very gratifying that Dr. Davenport and, from what we have just heard, 

 also Dr. San Pietro, find that phosphorylation increases the rate of TPN reduction, 

 because this brings into agreement the facts of non-cyclic photophosphorylation 

 with TPN with the earlier observations of the ferricyanide system. Aly question is 

 whether you have tested any connection between the pyridine nucleotide reductase 

 and the photosynthetic cytochromes ? 



D.'WENPORT: Well as you know the problem of looking at cytochromes in the 

 presence of chlorophyll is one which, as far as I know, has not been solved unless 

 Dr. Chance can tell us how it can be done, so I cannot say. 



Chance : Here, I cannot solve the problem of photosynthetic cytochromes but 

 I can mention some very preliminary experiments with Dr. San Pietro who was 

 good enough to work with us on PPNR, and to investigate whether bleaching 

 actually occurs in the presence of the chloroplasts. We did find the pigment in 

 PPNR to be bleached. We found a difference spectrum on illumination of roughly 

 23 ^moles PPNR and roughly 25 /(moles are bleached in the absence of TPN. 

 If TPN is present, bleaching is much less. The rate at which the absorbancy 

 change occurred was in rough agreement with the rate at which TPN was reduced ; 

 so it is not unreasonable to believe that this absorbancy change has something to 

 do with the activities. But it is obvious that the spectrum doesn't identify the 

 compound involved. 



