INTRODUCTION 



The investigation of reaction kinetics, i. e., of the dependence of rate 

 on various external factors, has acquired a greater importance in the study 

 of photosynthesis than in that of other biochemical processes. Faced with 

 the failure of the usual qualitative methods of biochemistry to disentangle 

 the complex mechanism of photosynthesis, many investigators turned to 

 rate measurements, hoping that the number, sequence and character of 

 the partial processes involved in photosynthesis could perhaps be derived 

 from such studies. The results did not quite satisfy expectations, for 

 reasons not difficult to understand. What one measures as the "yield of 

 photosynthesis" is the net result of the operation of a complex mechanism. 

 No simple kinetic equation can account for all the factors that influence 

 this yield. It is comparatively easy, after having made a series of kinetic 

 measurements on a selected object, to invent a model that would interpret 

 these particular observations, or even to write down equations fitting the 

 experimental results more or less closely. The literature on photosynthesis 

 abounds in such formulations. Their limited significance is illustrated by 

 the fact that practically nobody ever uses equations derived by somebody 

 else; instead, every investigator starts anew, often without as much as 

 referring to his predecessors, and — what is even more unfortunate — without 

 making an attempt to correlate his formulae with any experimental results 

 but his own. 



Photosynthesis is such a complex and heterogeneous process that it is 

 probably impossible to make a complete analysis of its mechanism merely 

 by measuring the rate of the over-all process under different conditions. 

 However, this does not mean that kinetic measurements of photosynthesis 

 are useless ; but rather that they are most useful when combined with other 

 biochemical and biophysical methods of approach, such as the use of poisons 

 and narcotics, provision of substitute reductants and oxidants, or partial 

 tearing down of the photosynthetic apparatus (e. g., by the separation of 

 chloroplasts from cytoplasm). Several investigators have already used 

 measurements of the intensity of chlorophyll fluorescence as an auxiliary 

 physical tool to supplement chemical rate measurements; it may prove 

 possible to make similar use of absorption and fluorescence spectra, of 

 radiochemical and perhaps also electrochemical measurements, to provide 

 "running comment" on the state of the photosynthetic apparatus during 



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