190 



Achim Trebst, Herbert Eck and Sieglinde Wagner 



addition of o,2 /imol of M^T'oI TPNH formed 



0,5 



plastoquinone-45 ^ > ° 



plastoquinone-15 ''» ' 



plastoquinone-5 ^'" 



2 , 3 -dimethyl -phytylbenzoquinone 3 > ^ 



2 , 3 -dimethyl - 5 - allylbenz oquinone o > o 



2 , 3-dimethyl-benzoquinone o> ° 



2,3-dimethoxy-methylbenzoquinone o. ^ 



2,3-dimethyl-benzoquinone-butyric acid o. 5 



ubiquinone-5o °»^ 



Table 15: Reactivation of TPN reduction by quinones in petrolether extracted 

 chloroplasts (exhaustively extracted, o,3 ml dialyzed, watersoluble 

 chloroplast extract added, 15 min light in N^). 





 II 



J II II 



H 

 



R = -CH2-GH=C.Qj^^ -CH2-CH=C.g -CH2-CH2-CH2-COOH 



5 

 -5-dimethyl-allyl -5-allyl -5-butyric acid 



(plastoquinone-5) 



plastoquinone-45 no no 



activity "^ 



Besides two methyl-groups in position 2 and 3, a substitution at position 

 5 by -CH2-CH=C-(CH3)2 seems to be essential for the activity at the first plasto- 

 quinone site in the electron transport chain of photosynthesis. 



Krogmann and Crane ° also showed that different photosynthetic re- 



actions of chloroplasts have different structural requirements in their reacti- 

 vation, after endogenous plastoquinone has been extracted. 



The following scheme is to indicate the proposed two sites of plastoqui- 

 none function and the site of salicylaldoxime inhibition as discussed in the pre- 

 ceding chapters. 



