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Birgit Vennesland 



not conJ-ain much activated CO^. However, when this vessel was illumi- 

 nated, there was a pressure burst due to the release of excess 0«. In steady- 

 state photosynthesis, O^ evolution is accompanied by an equivalent CO^ 

 consumption, but here O^, evolution exceeded CO„ consumption by an a- 

 mount approximately equivalent to the amount of activated CO^. In sum- 

 mary, when the cells are incubated in air and CO^ in the dark, they form a 

 CO^ compound which is readily converted to 0_ in the light, but which 

 readily decomposes to CO^ in the dark. Since we don't know the chemical 

 structure of this substance, we represent it by the symbol CO„. Because it 

 is split to O^ in the light, it has also been called the "photofyt". The con- 

 clusive proof of the Importance of CO„ is the demonstration that It decom- 

 poses to O^ with a quantum requirement of one^ '. The photosynthetic unit 

 Is one. One molecule each of chlorophyll, glutamate and CO^ form a 

 complex which liberates O^ when it absorbs a photon. The reducing power 

 generated by the light resides in the reduced carbon left behind by O^ 

 elimination. 



It has been claimed that there is no such thing as activated CO_ — ex- 

 periments with C'^ are said to reveal no trace of it^"^'. In this connection I 

 must emphasize that CO^ is consumed as fast as It Is formed when the cells 

 are strongly illuminated. Cells performina photosynthesis at maximum rates 

 contain little CO„. If you want to use C to show that there is no such 

 compound you win of course use a bright light. Cells operating at maxi- 

 mum efficiency must, on the other hand, keep the photolyt reservoir full . 



Since there isn't enough energy in one photon of red light to convert 

 one molecule of CO„ to 0„ and carbohydrate, the energy deficit must be 

 made up. The manner In wTiich this occurs was made clear by the discovery 

 of the light-induced respiration. This phenomenon is quite easy to demon- 

 strate manometrlcally with Chlorella. Those who wish to see it may be ad- 

 vised not to use too heavy a cell suspension, or most of the cells will be in 

 the dark most of the time, so that most of the light-induced respiration may 

 occur during the illumination period^ I 



At this point, it is appropriate to mention the use of labeled oxygen to 

 measure the light-Induced respiration. One would expect to see more of 

 this respiration with the 0'° technique than one can see manometrlcally. 

 But it is not true that the use of the O technique will guarantee that one 

 sees all of this light-Induced respiration. The method requires a sampling 

 of oxygen from a gas phase, supposedly In equilibrium with the inside of the 



