NUCLEOTIDES AND MITOCHONDRIAL FUNCTION 23 1 



These results show that added ATP can influence the redox state of 

 intramitochondrial components of hydrogen transfer such as DPX and 

 flavoprotein. It is to be assumed that ATP exerts its influence through back 

 reactions of oxidative phosphorylation. The energy requirement for the 

 DPX reduction in the presence of succinate or glycerolphosphate — so far 

 only postulated on the basis of thermodynamic reasoning — has been 

 directly demonstrated bv these experiments. This phenomenon appears to 



340- 

 380 myu 



DPN 

 reduction 



capronat 



Fig. 2. The reducing effect of ATP on mitochondrial pyridine nucleotides 

 in the presence of non-DPN-linked substrates. Double beam spectrophotometer 

 recordings of suspensions of mitochondria, a. Skeletal muscle mitochondria, 2 • 8 

 mg. protein ml. b. Heart muscle mitochondria, 2-0 mg. protein/nil. Incubated in 

 0-3 M sucrose, i mM EDTA, 10 m.M triethanolamine-HCl-buffer, pH 72, 25 , 

 air-saturated. 



apply to all substrates that can transfer hydrogen to the respiratory chain 

 without a participation of DPX, since also with fatty acids DPX can be 

 reduced at the expense of energy supply from .A.TP. In agreement with 

 this picture no ATP is required for the reduction of DPX with DPX- 

 specific substrates such as pyruvate plus malate. 



Further work may be mentioned which was aimed at exluding other 

 possible explanations of this ATP effect. Thus the specificity for ATP and 

 the studies on the conditions for the ATP-effect furnished additional 

 evidence that ATP acts in a reversal of oxidative phosphorylation [15]. 



In particular, the question arises why ATP is required for DPX reduc- 

 tion in isolated skeletal-muscle mitochondria in contrast to mitochondria 



