NUCLEOTIDES AND MITOCHONDRIAL FUNCTION 233 



uncoupling of the mitochondria. In consequence, now the endogenous 

 oxidative phosphorylation is more efficient in supplying energy for DPN 

 reduction. No external ATP is required any more, since addition of ATP 

 in this case would not increase the DPN reduction. As shown further in 

 the experiment of Fig. 3, DPNH becomes oxidized when respiration, and 

 thus oxidative phosphorylation, are inhibited by antimycin A. The energy 

 for DPN reduction now has to be supplied by external ATP. The experi- 

 ment shows, firstly, that for DPN reduction the oxidative phosphorylation 

 system has not only to be intact, but also operative. Otherwise, ATP 

 addition is required. Secondly, albumin acts only by protecting oxidative 

 phosphorylation. 



A similar reaction sequence can be observed with flavoprotein (Fig. 4). 

 The partial oxidation of flavoprotein on addition of antimycin A, which 



468-500m;< 



00025 



Flavoprotei 

 reduction 



"I 



Fig. 4. The effect of serum albumin, antimycin A and ATP on flavoprotein 

 in the presence of glycerol- 1 -phosphate (cf. legend Fig. 2.). 



was previously mentioned (cf. Table I), demonstrates that the reduction 

 of some flavoprotein depends on energy supply from oxidative phosphory- 

 lation. When inhibited, oxidative phosphorylation can be replaced by 

 added ATP, which then effects a reduction of flavoprotein in the same way 

 as with DPN. 



EFFECT OF ATP ON CYTOCHROMES AND RESPIRATION 



So far we have dealt with the influence of the ATP-level on the redox- 

 state of DPN and flavoprotein. By these experiments an action of ATP on 

 the DPN-flavin region only is conclusively demonstrated. That means 

 that these experiments show primarily the reversal of the first phosphory- 

 lation step of the respiratory chain. It has now been possible to demonstrate 

 also an influence of ATP on the redox state of the cytochrome region of 



