108 FACTORS AFFECTING METABOLISM in vitro 



see how these resuhs can be reconciled. With the intact tissue 

 shce, fluoride and iodoacetate are considered to act primarily upon 

 enolase and 3-phosphoglyceraldehyde dehydrogenase respectively 

 whereas malonate acts primarily by inhibiting succinic dehydro- 

 genase. Although concentrations of inhibitors reducing the oxygen 

 uptake of the slice make part of their action understandable in 

 terms of decreased rates of oxidative phosphorylation, the effec- 

 tiveness of low concentrations of iodoacetate in reducing phosphate 

 incorporation emphasizes the importance of the glycolytic pathway 

 in the maintenance of phosphate metabolism in the tissue. On the 

 other hand an uninhibited glucose metabolism, unconnected with 

 adequate levels of energy-rich phosphates appears to be insufficient. 

 This is illustrated by the action of 2 : 4-dinitrophenol and sodium 

 azide, agents which do not directly inhibit enzymes involved in the 

 metabolism of glucose, but specifically interfere with the mechan- 

 isms whereby phosphate is esterified to adenosine triphosphate 

 during oxidation. Their " uncoupling " action in cerebral slices is 

 accompanied by an increased oxygen uptake and an increased con- 

 sumption of glucose and production of lactic acid. At 10~^-10~^ M, 

 both dinitrophenol and azide reduced the levels of phosphocreatine 

 and the total energy-rich phosphates in cerebral slices (Mcllwain 

 and Gore, 1951; Kratzing, 1956), and also markedly decreased 

 phosphate incorporation into the phospholipids, nucleic acids and 

 phosphoprotein fraction. Of these two agents dinitrophenol was 

 the most effective, phosphocreatine levels being fully decreased by 

 10-5 M. 



Dispersions of cerebral tissues react somewhat differently 

 according to the type of preparation employed. Thus with 

 preparations containing mitochondria and carrying out oxidative 

 phosphorylation with pyruvate as substrate, fluoride at 10"^ M, 

 though decreasing the oxygen uptake slightly, resulted in an 

 increase in the specific radioactivity of the phospholipids 

 (McMurray et al., 1957) and phosphoprotein fraction (Heald and 

 Stancer, 1960). These results are probably attributable to the well- 

 known effect of fluoride in inhibiting adenosine triphosphatase 

 (Case and Mcllwain, 1951) for in such preparations levels of 

 adenosine triphosphate were higher in the presence than in the 

 absence of fluoride (McMurray et al, 1957; Berry and McMurray, 

 1957). With preparations where the labelling of phospholipids was 

 primarily a glycolytic mechanism, fluorides decreased such label- 



