SOME FLAVIN INTERACTIONS WITH GRANA 

 (SEEN IN A DIFFERENT LIGHT) 



Birgit Vennesland 



There are currently two completely different ways of conceptualizing the 

 mechanism of photosynthesis. One Is so familiar to you that I need not sum- 

 marize it. On the other hand, we have Warburg's view — shared by a mi- 

 nority and unfamiliar to many. I welcome this opportunity to elucidate 

 Warburg's point of view because, in my opinion, his picture of the mecha- 

 nism of photosynthesis Is right. 



Warburg's theories are. In a sense, summaries of the results of his ex- 

 periments. It is impossible to judge the theories without considering the ex- 

 periments on which they are based. To do this adequately in the allotted 

 time is Impossible. The experiments should be considered not only in detail, 

 but in toto; for the interpretation of a set of observations on isolated chloro- 

 plasts rests in part on what one has learned from a study of intact Chlorella. 

 I can't take time here to describe all the important experiments that War- 

 burg has done with Chlorella, but I'll compromise with necessity by out- 

 lining briefly a few facts which are particularly important as guides to the 

 Interpretation of the phenomena we study with isolated green grana. 



SOME EXPERIMENTS WITH CHLORELLA 



First, let me recall a set of experiments which show that CO^ is required 

 for the compensation of respiration by light ^ ' . If the CO„ proauced In 

 respiration Is removed rapidly, light cannot compensate respiration. The 

 experiment Is done manometrically, with a Chlorella suspension In the main 

 compartment of the Warburg vessel, and base in the side-arm. Under these 

 conditions, the effectiveness of light In counterbalancing respiration depends 

 on the rate of shaking. Rapid shaking ensures rapid removal of CO„ and 

 leaves the light nothing to work on. As the rate of shaking is decreased, 

 the light becomes Increasingly more effective. This experiment shows that 

 light exerts Its effect on the endogenous dark-respiration of Chlorella by 

 way of CO„. 



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