VOL. 12 (1953) 



BIOCHIMICA ET BlOPHYSICA ACTA 



347 



AN ELECTROCHEMICAL DEMONSTRATION OF THE ENERGY CYCLE 

 AND MAXIMUM QUANTUM YIELD IN PHOTOSYNTHESIS* 



by 



KURT DAMASCHKE, FRITZ TODT, DEAN BURK** and OTTO WARBURG 

 Max Planck Institute for Cell Physiology, and Material-prufungsamt, Berlin-Dahlem (Germany) 



A new and rapid electrochemical method with a time period of less than one second 

 has been applied to a study of the oxygen exchanges occurring in Chlorella cultures 

 during varying periods of darkness and of illumination with measured quantities of 

 visible light. It has been possible to show that an initial photochemical reaction takes 

 place with a high quantum efficiency, and that this photo reaction is followed by a back 

 reaction of enhanced oxygen consumption with a time period that may vary from 

 seconds to a few minutes. The overall efficiency of net oxygen production in this cycle 

 approaches, under suitable experi- 

 mental conditions, the theoretical 

 limit set by the first and second laws 

 of thermodynamics, namely, 2.5 to 

 3 quanta of light per molecule of 

 oxygen gas produced. 



METHODS 



The electrochemical measure- 

 ment of dissolved oxygen was carried 

 out by the method of Todt^-^ in glass 

 vessels of the type illustrated in 

 Fig. I. Such vessels had a volume of 

 80 ml or more, and a diameter of 

 6 cm, and hence an area of 28 cm^ 

 on the bottom surface, which the 

 measured light entered and covered 

 to the extent of at least 95 %. At the 

 top edge of a given vessel there were 

 three inlets with glass-ground joints, 

 two inlets for holding electrodes, and 

 a third inlet for holding either a 

 simple stopper or a microburette 



used in connection with electrode „. t^ 1 ^ , ^ , • , 



. l-ig. I. Vessel for electrochemical measurement of 



calibration lor oxygen response. oxygen exchange in photosynthesis and respiration. 



* The substance of this paper was presented in a lecture entitled T hermodynamik und Kinetik 

 der Photosynthese given by Dean Burk on July 6, 1953 at the Max Planck Institute for Medical 

 Research, Heidelberg, at the invitation of Prof. Richard Kuhn, Director. 



** Foreign Member, Kaiser Wilhelm Institut for Cell Physiology, Berhn-Dahlem, and Head of 

 Cytochemistry Section, National Institutes of Health, United States Public Health Service, Beth- 

 esda, Md. (U.S.A.) 



References p. 355. 



22 



