2s8 



DANIEL M. ZIEGLER 



reduced in ETP is the sum of the amounts obtained with either substrate 

 alone. We do not have an explanation for these phenomena but the results 

 demonstrate that the non-haem iron compounds are closely associated 

 with the flavoproteins in the electron transport system, since all of the 

 components after iron in the electron transport secjuence can be completely 

 reduced by either substrate. 



TABLE IV 



The Effect of Inhibitors on the Reduction of Non-Haem Iron in ETP 



Inhibitor 



Concentration 



Percentage of 



total iron reduced 



bv DPNH 



Percentage of 



total iron reduced 



by succinate 



None 



Amytal 



Malonate 



1 X lO" 



2 X lO 



39 

 o 



6S 



3 



59 



o 



The compound 2-thenovltrifluoroacetone which chelates with iron is 

 a highly efficient inhibitor of succinic-CoQ reductase activity (Table V). 

 The level of the inhibitor required to block the reduction of CoQ by the 

 reductase has only a small effect on the reduction of phenazine metho- 

 sulphate and does not affect, at all, the phenazine reductase activity of the 



TABLE V 



Inhibition of Succinic-CoQ Reductase Activity by 2-Thenoyl- 

 trifluoroacetone* 



Electron acceptor (percentage inhibition) 



Preparation 



CoQ 



Phenazine 

 niethosulphate 



Primary succinic flavoprotein [4] 

 Succinic-CoQ reductase [s] 

 ETP„[ii] 



97 



o-o 

 17 -o 

 i8-o 



* The final concentration of the inhibitor — i x 10 ^ m. 



primary succinic flavoprotein. These data demonstrate that this metal 

 chelating compound blocks a site required to link CoQ to the flavoprotein. 

 The reagent does not combine with the flavin since it does not aflPect the 

 phenazine methosulphate reductase activity of the primary succinic flavo- 

 protein. Thenoyltrifluoroacetone does not remove non-haem iron but 

 appears to form a strong complex with the enzyme-bound iron, which can 

 no longer undergo oxidation and reduction. These data are consistent with 



