TRICARBOXYLATE CYCLE 93 



sidered since 1940 as a specific inhibitor of the EM pathway in this concen- 

 tration range. 



The more recent work has also been consistent in establishing that pyru- 

 vate oxidation is reasonably sensitive to iodoacetate. It is necessary to pre- 

 sent these results briefly because this is one of the most important problems 

 in the use of iodoacetate and every effort must be made to determine the 

 maximal concentration which may be used without significantly depressing 

 pyruvate oxidation, since without this information it is impossible to use 

 iodoacetate as a selective inhibitor of the EM pathway. The oxidation of 

 pyruvate, lactate, and acetate is inhibited 100% by 1 niM iodoacetate in 

 Penicillium chrysogenum, and even 0.1 mM inhibits acetate oxidation 80% 

 (Hockenhull et al, 1954 b). The metabolism of pyruvate by yeast is in- 

 hibited 92% by 0:58 mM iodoacetate and 96% by 1.2 mM iodoacetate 

 whether Og uptake, CO2 formation, or pyruvate utilization is measured over 

 180 min (Runnstrom and Brandt, 1941). The inhibition develops rather 

 slowly and is not very marked during the first hour. It was concluded that 

 iodoacetate cannot separate the oxidation and decarboxylation of pyruvate. 



The uptake of pyruvate by Chlorella elipsoida is more sensitive than the 

 respiration to iodoacetate (see accompanying tabulation) (Oaks, 1962). A 



concentration of iodoacetate which abolishes glucose respiration does not 

 affect pyruvate respiration, but inhibits the pyruvate uptake and the ratio 

 of C^^Oa obtained from pyruvate- l-C^'' and pyruvate-S-C^^. The cells were 

 treated 2 hr with iodoacetate. The 0^ uptake due to pyruvate in barley 

 roots is inhibited progressively by 0.04 mM iodoacetate, the degree of inhi- 

 bition depending on the time and the pH (see page 1-724) (Laties, 1949 a). 

 If pyruvate is added with the iodoacetate it increases the respiration strong- 

 ly, but if added at varying times after the addition of iodoacetate the re- 

 spiratory stimulation becomes progressively less. It was postulated that 

 perhaps pyruvate can protect pyruvate oxidase. 



The results in animal tissues are quite comparable to those found in 

 microorganisms and plants. Marshall (1948) showed that the respiration of 

 Plasmodium-psiTaisitized chick erythrocytes in the presence of pyruvate or 

 lactate is inhibited 75-85% by 0.9 mM iodoacetate. Webb et al. (1949) 



