Enzymes 55 



(Dawkins et al., 1959) . The basic injury here consists in depriving 

 the cell of its blood supply. 



An isolated unperfused liver rapidly loses its ability to oxidise 

 the substrates of the tricarboxylic acid (TCA) cycle. The oxidation 

 of succinate by succinic dehydrogenase is an exception, and is main- 

 tained for some time. This failure of oxidation is at least partly due 

 to loss of the coenzymes, e.g., DPN and TPN which, as described 

 above, are closely involved in respiration. The importance of these 

 substances is shown by the ability of added DPN to maintain oxida- 

 tion of substrates such as pyruvate. It is of interest, too, that oxida- 

 tion of succinate to fumarate does not require the presence of the 

 pyridine nucleotides as coenzymes. Even more rapid than failure 

 of oxidation is the loss of oxidative phosphorylation, i.e. the syn- 

 thesis of ATP. This change occurs within a few minutes of in- 

 cubating the isolated liver at 38°. Other abnormalities that develop 

 are loss of potassium and intracellular accumulation of sodium, 

 calcium and water. 



The early failure of oxidation and oxidative phosphorylation 

 may be prevented by perfusion of the liver with glucose or with a 

 tricarboxylic acid cycle substrate such as glutamate. In the presence 

 of glucose oxygen is not required. 



The interpretation of these experiments is not simple but it 

 seems likely that the basic and earliest failure is loss of the ability to 

 synthesise ATP due to lack of substrates for the processes of glycoly- 

 sis and oxidation and to loss of the coenzymes also required for these 

 complex reactions. Inability to synthesise ATP leads to failure of 

 oxidative phosphorylation and thus to loss of the cell's supply of 

 energy. This is followed in turn by further loss of coenzymes due 

 to inability to synthesise them, by profound disturbances in water 

 and electrolyte movements and by a general failure of those reac- 

 tions which depend upon ATP for an energy supply e.g., the syn- 

 thesis of proteins and phospholipids. 



Mitochondria isolated from liver cells, and then incubated in 

 vitro show degenerative changes similar to those observed in the 

 parent tissue. Mitochondria are the chief intracellular seat of res- 

 piratory activity and of the associated generation of energy. On 

 incubation they show a rapid loss of oxidative phosphorylation 



