THE MECHANISM OF COENZYME Q REDUCTION IN HEART MITOCHONDRIA 26 1 



Q2 in some of this work because it is far more soluble than Qm, and in this way 

 we can eliminate the necessity of adding the extra phospholipids required to 

 solubilize Qio, but we can always replace the Q., with Qio plus phospholipids, and 

 we have not detected a difference in specificity in the reduction of Qo or Qk, by 

 succinate. 



Chance: I was struck by the small degree of reduction of the iron in the 

 various preparations in spite of the fact that they are inhibited by cyanide or 

 antimycin A. Under these conditions I believe all the flavin would be reduced, and, 

 if they contain Q, that would be similarly reduced. So do you have an explanation 

 of values of only 30 to 60*',, reduction of the iron ? 



Ziegler: Some data which I did not show indicate that if you add both sub- 

 strates to an ETP, which contains the two intact chains, the total amount of iron- 

 reduced summates. DPNH reduces between 25 and 45^0 of the iron and succinate 

 reduces about 30*^0; if you add both substrates 60 to 7o"o of the iron is reduced. 

 Chance: This is however considerably smaller than the percentage reduction 

 of Q, and thus suggests that not all the non-haem iron is active in the pathway 

 you are considering. 



Ziegler: Yes, I would agree that not all of the iron functions in this capacity. 

 Chance : How many atoms of iron per molecule of Q are there ? 

 Ziegler: In ETP there is twice as much non-haem iron as Q. In other words, 

 per electron equivalent they are almost equal. 



Chance: I am still not clear how many irons per Q are in the electron transfer 

 pathway. 



Ziegler : This would be a very difficult question to answer at this time since 

 we do not know how much of the endogenous Q is involved in the oxidation of 

 either succinate or DPNH. A more pertinent question would be, how many irons 

 per flavoprotein are involved in the pathway to Q, and in all of our preparations 

 capable of reducing Q at least 2 moles of iron per flavin undergo oxidation and 

 reduction. In ETP the ratio of reducible iron to flavin is much greater than 2 and 

 with both succinate and DPXH present the ratio can be as high as 15. 



EsTABROOK : On the same point, I was wondering whether you have an explana- 

 tion for your table (p. 258) of inhibitors where you show that when you used 

 succinate as a substrate in the presence of amytal, which is an inhibitor of DPNH 

 oxidation, you get the sunimation of iron reduced. In the same way as in the 

 presence of malonate with DPNH as a substrate, you also find this summation. 

 Ziegler: I have no adequate explanation for these phenomena. 

 Singer : Your slide shows eight atoms of iron per mole of flavin but, if I am 

 not mistaken, your publication on the highly purified enzyme showed the same 

 ratio as in the flavoprotein itself, that is four to one, and I am wondering what has 

 happened in between to change these analytical data and whether this might 

 throw some light on Dr. Chance's question. 



We have been studying for some years the transformations that occur during 

 the extraction of succinic dehydrogenase from the respiratory chain preparations. 

 Since our results are relevant to the function of the metal in this enzyme, I might 

 sum up the salient points. There are three main differences in the behaviour of 

 succinic dehydrogenase between particulate (respiratory chain-bound) prepara- 

 tions and soluble ones. One is that the dehydrogenase is cyanide-sensitive in 



