43 



Bessel Kok 



faster method Witt et al. (7) still fail to observe the reduc- 

 tion of cyt. f, presumably carried out by a dark step follow- 

 ing the second photoact. (Spectroscopic measurements which 

 use continuous actinic illumination cannot discriminate be- 

 tween compounds directly involved in the electron transport 

 chain and those which are indirectly affected.) Unless one 

 considers a complete re-interpretation of available data, one 

 must assume that the early events in photosynthesis occur 

 with such extreme rapidity that they escape observations with 

 present methods. Also, this feature seems to leave_little 

 room for an intermediate electron transport chain Y — > P . 



Finally, one cannot help drawing an anology between the 

 (copper and haem containing) cytochrome oxidase in respira- 

 tion and the peculiar combination of plastocyanin and cyto- 

 chrome f in photosynthesis (cf. section III) — reason why we 

 have suggested in scheme Fig, 5 that photosynthetic oxygen 

 evolution might be a light driven reversal of the terminal 

 respiration step (4). 



Presently, the evidence concerning the photosynthetic 

 light reactions is so much in flux and of qualitative nature 

 that the speculations forwarded do not appear too much out 

 of line. 



V. Acknowledgements 



The author gratefully acknowledges the collaboration of 

 Mrs. Pat VVoolf and Mr. Hans Rurainski. 



The work reported was supported in part by the National 

 Institutes of Health, the Air Force Office of Scientific 

 Research, the Air Force School of Aerospace Medicine and 

 the National Aeronautics and Space Administration. 



