FUNCTION OF FLAVOENZYMES IN ELECTRON TRANSPORT 



149 



DPNH oxidation in liver mitochondria this does not imply that Alartius's 

 original idea [29] of the participation of vitamin K in the main respiratory 

 chain need to be abandoned. Indications of a specific role of vitamin K in 

 DPN-linked respiration and phosphorylation have been reported, both in 

 fractionated bacterial systems [30] and in U.V. -irradiated liver-mito- 

 chondrial preparations [31, 32]. Even if this evidence is only circum- 

 stantial, its validity is not influenced by the present conclusions. It may 

 well be that bound vitamin K does participate as an electron carrier in the 

 amvtal-sensitive, main pathway of mitochondrial DPXH oxidation. 



DPNH 



TPNH 



Amytal 



Antimycin A 



Dicoumarol 



Fig. 6. Rtlation of DT diaphorase to the main pathway of DPXH oxidation 

 of intact liver mitochondria. Fp]j = DPXH diaphorase; Fpi,T — DT diaphorase. 

 Dotted arrows indicate pathways involving externally added carriers. 



located, tentativelv, between the DPXH diaphorase and cytochrome b. 

 Such a possibilitv mav actually find some indirect support in our data, 

 which indicate that cytochrome /; might require a 2-methylnaphtho- 

 quinone as a specific electron donor. Pertinent to this possibility may also 

 be the preliminary findings, illustrated in Table VII, that the DPXH 

 diaphorase reaction of the Kielley and Kielley preparation reveals a marked 

 sensitivity to amytal when measured with 2-methyl-substituted quinones 

 as electron acceptors, whereas it exhibits only a slight amytal sensitivity 

 with non-substituted quinones. Thus, the role of vitamin K in respiration 

 and phosphorylation deserves further consideration. 



A second point of interest is that of the well-known uncoupling effect 



