AEROBIC METABOLISM OF CARBOHYDRATE 



109 



tiated by the low respiratory inhibition at 0.01 mM. As the iodoacetate con- 

 centration is increased, the EM pathway is depressed more, and the pyruvate 

 concentration reaches the level where it becomes limiting to its oxidation; 

 at this point respiration is inhibited, as seen by the sudden rise in inhibi- 

 tion at 0.01-0.04 mM iodoacetate. There may also be some slight direct 

 inhibition of pyruvate oxidation so that the concentrations of pyruvate and 

 lactate do not change significantly. Finally, when the iodoacetate concen- 

 tration is such as to block the EM pathway essentially completely, the lac- 

 tate concentration falls again. Other equally tenous explanations could be 

 easily adduced. 



0.02 



IODOACETATE 



0.06 



Fig. 1-10. Effects of iodoacetate on aerobic glycolysis 



and respiration of guinea pig brain slices. (Data from 



Heald, 1953.) 



Endogenous Respiration 



The effects of iodoacetate on the endogenous respiration provide little 

 information on either the site of iodoacetate action or the nature of this 

 respiration, although occasionally some indication of the principal endoge- 

 nous substrate is obtainable if the experiments are properly run. However, 

 it is very important to determine the inhibition of the endogenous respi- 

 ration if the action of iodoacetate on the oxidation of some added sub- 

 strate is being examined, since correction for the endogenous effect must 

 be made (1-441). Such a correction has been used very little in the work 

 with iodoacetate and glucose oxidation. Selected examples of the inhibition 



