NUCLEOTIDES AND MITOCHONDRIAL FUNCTION 



229 



nucleotide system is compared with the redox states of the pyridine and 

 flavin nucleotide systems under various conditions, as shown in Table I. 

 These data have been obtained by enzymatic analysis. The mitochondria 

 are saturated with substrate in the presence of oxygen and thus are in a 

 condition facilitating the phosphorylation of the endogenous adenine 

 nucleotides. The data refer to a steady state. The substrates can be 

 divided into two groups : the DPX-specific substrates, pyruvate plus malate, 



TABLE I 



Nucleotide Systems in Mitochondria 



Comparison between the phosphorylation state of the adenosine phosphates 

 and the redox state of DPN and fiavoprotein. 



* Z-AP^ATP + ADP + AMP. 

 t rDPN = DPN + DPNH. 



J Calculated from extinction changes at 468-500 m/t, using Jen-,;^, = 8-5 cm~^. 



and the non-DPN-specific substrates, succinate and glycerol phosphate. 

 The postulated energy supply for the succinate or glycerol-phosphate 

 linked DPN reduction might be reflected in the intramitochondrial ATP- 

 level. However, with both these groups of substrates about 50-70% of the 

 adenine nucleotides are present as ATP. Addition of phosphate on top of 

 the endogenous phosphate increases the phosphorylation, as is to be 

 expected. In contrast, there are large difl"erences between the two groups 

 of substrates with respect to the degree of reduction of the DPN. With 

 succinate or glycerol phosphate, DPN is reduced to a greater extent than 

 with pyruvate plus malate. These results show that the redox state of the 

 mitochondrial DPN appears not to be only a function of the endogenous 

 energy supply, as expressed in the phosphorylation state of the adenine 



