Introduction 39 



Let a quinone be the catalyst, then the equations of light-induced respiration 

 are: 



But if the balance of light-induced respiration is zero, how can light-induced 

 respiration be discovered ? In the dark it cannot be discovered, because in the dark 

 it does not occur. In light it cannot be discovered, because in light the produced 

 carbon dioxide is split according to equation [4] into C — O2. 



Yet it has been possible to discover and to measure light-induced respiration. 

 If to a Suspension of illuminated grana as much hydrocyanic acid is added that the 

 catalase of the grana is inhibited, then in reaction [2] the double amount of oxygen 



IS COnsumed : 2 2 - 2 hydroquinone = 2 quinone + 2 H 2 2 



and two molecules of hydroperoxide are formed for each molecule of oxygen devel- 

 oped. Then the balance of the equations [1] to [5] is no more zero but becomes: 



2 + 2 HoO = 2 H2O2 



This means that light-induced respiration can be measured by the consumption of 

 oxygen and by the production of the double amount of hydrogen peroxide ; a 

 method that has been possible owing to the fact that oxygen development in illu- 

 minated grana is not inhibited by hydrocyanic acid. In this way light-induced 

 respiration of the grana has been discovered and the energy problem of the grana 

 reactions has been solved. 



Light-induced respiration may also explain in a simple way why grana cannot 

 fix carbon. Let us assume that in illuminated grana the oxidation of reduced carbon 

 dioxide proceed quickly in comparison to the reduction of carbon dioxide and that, 

 inversely, in illuminated cells, reduction proceed quickly in comparison to oxi- 

 dation, then we may understand why darkening produces in cells, but not in grana, 

 a gain of reduced carbon dioxide, that is, fixation of carbon. 



The third point — that oxygen development in illuminated grana is not inhibited 

 by hydrocyanic acid — is still mysterious. We have no idea how to explain the dif- 

 ferent behavior of cells and of grana toward hydrocyanic acid. 



