189 



Achim Trebst, Herbert Eck and Sieglinde Wagner 



^mol electrons transferred 



without with 



the addition of 

 0,2 ^mol plastoquinone 



5 fxmol TPN 



lo /xmol ferricyanide 



0,2 /xmol 2,3-dimethyl-benzoquinonebutyrate 



0,2 fxmol 2,3-dimethoxy-methylbenzoquinone 



0,2 ^mol vitamin K^ 



0,2 jLimol anthraquinone- sulfonate 



2 , o 

 0,1 

 1.8 

 2.1 

 0,1 

 0.1 



2.1 

 2,2 

 2.2 

 2.2 

 2,8 

 2,5 



Table 13: Plastoquinone dependence of the reduction of TPN. ferricyanide and 

 quinones in petrolether extracted chloroplasts (only 7o% of endoge- 

 nous plastoquinone removed). o,3 ml dialyzed. watersoluble chloro- 

 plast extract was added in the TPN experiment; quinone reduction 

 was measured by H7O2 formation in the presence of lo'^m KCN. 

 15 min light in air l^°) . 



The ferricyanide system in such incomplete extracted chloroplasts can 

 be reactivated by numerous p-benzoquinones . some of which are shown in table 

 14. There seems to be no structural requirements in the reactivation of the 

 second plastoquinone site, except that it has to be a substituted p-benzoquinone. 



addition of o,2 j^mol 



p -b enz oquinone 



2 , 3 -dimethoxy-p-benz oquinone 



2 , 3 -dimethoxy - methylb enz oquinone 



2 . 3 -dimethyl-p-benz oquinone 



2 . 3 -dimethyl -b enz oquinone -butyric acid 



tr imethyl -b enz oquinone 



p-benzoquinone-2 , 5-diacetic acid 



vitamin K_ 



jLimol ferricyanide reduced 



0,8 

 1,0 

 3.8 

 3,7 

 3,8 



4,1 

 4,2 

 4.4 

 0,9 



Table 14: Reactivation of ferricyanide reduction in petrolether extracted 

 chloroplasts (only 7o% of endogenous plastoquinone removed). 

 1 5 min light in N . 



Table 15 shows that after exhaustive extraction of plastoquinone the TPN 

 system is now also plastoquinone dependent (at site one). The reactivation of 

 this plastoquinone site is very specific. Only dimethyl-substituted benzoqui- 

 nones with an isoprenoid side chain of at least 5 C-atoms are active. 

 Allyl- as well as butyrate substitution in position 5 show no activity. 



