26 



B. Rumberg, P. Schmidt-Mende , J. Weikard and H.T. V/itt 



V. A POOL OF PHOTOACTIVE FLASTOQUIHONE 



From the magnitude of absorption changes of Chl-aj at 7o3 mu 

 and of Q at 254 mu it follows (together with the extinction co- 

 efficients of pure chlorophyll and pure plastoquinone) the ratio 

 of Chl-a-^: Q « 1 : 4. Q is the photochemical engaged plastoqui- 

 none; the total amount of plastoquinone is ten times higher (22)- 

 This means that there exists a pool (reservoir) of photoactive 

 plastoquinone between both light reactions (s. fig. 21) shuttling 

 electrons from reaction centre I to II. This result is also in 

 accordance with the fact that after extraction of plastoquinone 

 this substance can be recondensed into the same position. This 

 seems to be possible only when there exists a gap between reac- 

 tiion centre I and II which is filled up with larger amounts of 

 plastoquinone. The redox potential of this pool is probably con- 

 trolled by oxidants (Op) as well as by reductants. This pool 

 seems to be the reason for most of the so-called "induction pho- 

 nomena" in photosynthesis. 



VI. REAC TION MECHANISM OF THE OVER ALL PROCESS 



The coupling of reaction cycle I and II leads to a reaction 

 scheme of the over all process of the electron transport in pho- 

 tosynthesis which is mapped out in (1o)(1). An intermediate bet- 

 ween both cycles is probably cytochrome. This was demonstrated 

 in (ia(4)(1o)(1). 



