FUNCTION OF FLAVOENZYMES IN ELECTRON TRANSPORT 1 47 



and benzoquinones, only vitamin K3, out of a great number of quinones 

 tested, was able to carry out the above described by-pass of the mito- 

 chondrial amytal-sensitive site. This phenomenon is illustrated in Table 

 VI. It can be seen that there was a clear requirement for both the naphtho- 

 quinone skeleton and the 2-AIe substituent when the mitochondrial 

 respiratory chain served as terminal electron acceptor. This requirement 



TABLE VI 



Requirement for 2-Methyl-i,4-naphthoquinone Structure in Mediation of 



Electron Transport between DT Diaphorase and Mitochondrial 



Respiratory Chain 



(from Conover and Ernster [22], and unpublished data) 



* The quinones were used in final concentrations of 33 or 67 fiM as terminal 

 acceptors, and 8-33 or 10 /xM as mediators. 



t This activity was about i 5 times that obtained with DCPIP as acceptor. 

 + System I : Intact mitochondria, glutamate, amytal. 



System II : Submitochondrial DPNH oxidase (Kielley and Kiellev, light 

 pellet), TPNH, purified DT diaphorase, KCN. 



was valid both for intact mitochondria and for the reconstructed submito- 

 chondrial system, thus eliminating effects due to permeability barriers. 

 With purified cytochrome c, coupling occurred with both 2-Me substituted 

 and non-substituted naphthoquinone, and to some extent also with 2-Me 

 benzoquinones. The general rule that we presently envisage, after having 

 tested a large collection of quinones, is schematically illustrated in Fig. 5. 



