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BIrgit Vennesland 



interpret-atlon of the flavin reaction, which we make as shown in the fol- 

 lowing equations. In which F represents flavin, and E represents energy. 



(1) 



(2) 



(3) 



(4) 



(5) 



The photochemistry starts with reaction 1 . This is followed by the re- 

 duction of flavin as shown in reaction 2. But there is not enough energy in 

 one photon of red light to support a net reduction of two molecules of fla- 

 vin with evolution of one molecule of O^. To make up the deficit we pos- 

 tulate that half of the reduced flavin is reoxidized, as shown in equation 3 

 where E represents the decrease of free energy which occurs in the reaction. 

 This energy is used for the resynthesis of photolyt (equation 4). By summing 

 equations 1 through 4 we get equation 5, the reduction of one molecule of 

 flavin with one quantum of light. 



A few words of explanation are in order here. A set of equations such 

 as these are not intended to represent details of chemical mechanism. When 

 we know the details, we will insert them. Of course, equation 3 must be 

 chemically linked with equation 4. Of course, one can invent variations 

 on this theme, in great variety, and add postulated detail, fitting various 

 components of the respiratory chain onto various segments of these reac- 

 tions. All we are trying to do here is to construct a skeleton-framework 

 which we regard as correct in principle. 



We expect difficulty in detecting reaction 5, because FH- and 0_ will 

 back react. I have never been able to drive any O^ Into the argon gas 

 phase by Illuminating any amount of chloroplasts with any amount of flavin. 



One detail which I have not Inserted into equations 1 to 5 is the fact 



that the autoxidatlon of reduced flavin leads to the formation of H^O^. In 



ucl 



'2' 



2 2.' 

 such a back reaction one consumes twice as much O^ as Is formed. Irthe 



H„0_ is Immediately decomposed by catalase, this might make no 



