FUNCTION OF FLAVOENZYMES IN ELECTRON TRANSPORT 



159 



fluoride gave a similar efl^ect. This ATP-effect may be analogous to the 

 eff"ect of ATP in inducing DPN-reduction by succinate, recently observed 

 by Chance and Hagihara [45] in aged pigeon-heart mitochondria. 



It was brieflv indicated above (Table IX) that oligomycin A did not 

 inhibit (in fact even slightly stimulated) the succinate-linked reduction of 

 acetoacetate in the present system. As shown in Fig. 12, this compound 

 was also able to restore efficiently acetocaetate reduction when this was 

 suppressed because of the presence of a terminal phosphate acceptor (in 

 this case ADP, hexokinase and glucose). Oligomycin A has been shown by 



20 



16 



12 3 4 5 



/iq Oligomycin A 



Fig. 12. Effect of oligomycin A on succinate-linked reduction of acetoacetate 

 in presence of terminal phosphate acceptor (Azzone, Ernster, and Weinbach, 

 unpublished). Experimental conditions as in .ATP-hexokinase-glucose system in 

 Table VIII. 



Lardy et al. [46] to inhibit mitochondrial respiration under phosphorvlating 

 conditions but not if the phosphorylation is abolished by dinitrophenol ; in 

 extending these studies we found that oligomycin A onlv inhibits tightlv- 

 coupled, but not "loosely-coupled", respiration. Furthermore, according 

 to Lardy et al. [46], oligomycin A also strongly inhibits the mitochondrial 

 P,-ATP exchange and dinitrophenol-induced ATPase reactions. From 

 these observations, oligomycin A appears to act by blocking the transfer of 

 phosphate from the primary high-energy bonds to ADP. This mode of 

 action fits logically with the present findings that oligomycin A removed 

 the phosphate acceptor efi^ect from the succinate-linked reduction of 

 acetoacetate. What is more interesting, however, is that the transfer of 

 energy from the sites of the succinate-linked phosphorylations to the site 



