FUNCTION OF FLAVOENZYMES IN ELECTRON TRANSPORT 



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restored to its original level by the addition of ATP. From these and other 

 findings, the hypothesis was advanced that mitochondria, above a certain 

 level of structural organization, require ATP for oxidizing succinate, and 

 that, at this transitional stage of ageing, the mitochondria had already lost 

 their endogenous ATP while they still possess part of their organized 

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 min. preincubation 

 Fig. 7. Effect of ageing on succinoxidase activity of rat liver mitochondria (from 

 Ernster and Low [33]). The continuous lines indicate oxygen (upper line) and 

 phosphate (lower line) uptake in absence of ATP and Mg++; the large circles indicate 

 oxygen uptake, and the large triangles phosphate uptake, in presence of ATP and 

 Mg++. 



These findings were almost forgotten when last winter Dr. Azzone in 

 our laboratory made the interesting obser\ation [(y] that rat liver mito- 

 chondria after preincubation in the presence of 2 mM arsenate and o • 04 mM 

 dicoumarol (or o- 1 mM dinitrophenol) for a period of 3 to 4 min. displayed 

 a strongly inhibited succinoxidase activity, which could be greatly en- 

 hanced by added ATP. In extending this obser\ ation (which is illustrated 

 in the upper part of Fig. 8) it was found [7] that the decrease of the succin- 

 oxidase activity was correlated with an exhaustion of the endogenous high- 

 energy phosphate content of the mitochondria; and conversely, that any 

 means of pretreating mitochondria so as to deplete them of high-energy 



