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DISCUSSION 



Magasanik : In intact mitochondria the flow of electrons is controlled 

 by vitamin K. What prevents the other pathway from functioning? 

 You have not postulated any particular inhibitors ; is there any evidence 

 that something is produced in the vitamin K pathway that would tend 

 to inhibit the cytochrome c reductase pathway? 



Martius : I do not know. 



Potter: Is there any available information about the Michaelis con- 

 stants, for instance, for DPNH and cytochrome c reductase versus 

 vitamin K reductase? 



Martius: The constants have not yet been determined as far as 

 vitamin K reductase is concerned. 



Lehninger: The uncoupling in the two major spans of the chain is 

 interesting since both have the same sensitivity to dicoumarol as your 

 purified enzyme. In other words, 10~^ m produces virtually complete 

 uncoupling at all three levels in the chain. It is possible that there are 

 two actions of the compound. An alternative explanation may be that 

 vitamin K may not be in the respiratory chain per se, but may be "para- 

 sitic" at three different points. 



Siekevitz: Another explanation could be that there are quinones 

 besides the vitamin K, which come in at the cytochrome c level, or even 

 at the succinic dehydrogenase level. 



Krebs : If it occurs at three levels, as you suggest, would it mean that 

 these three substances must have different oxidation-reduction poten- 

 tials appropriate to the level at which they were operative? I suppose 

 that would be necessary and it would also be feasible. 



Lehninger: It is a different way of looking at the mechanism of 

 uncoupling and phosphorylation. It is remarkable that different 

 vitamin K derivatives have different O-R potentials. It might con- 

 ceivably fit in at three different levels. 



Lipmann: I have wondered about these three levels and the all-or- 

 none effect of the uncouplers. I think Dr. Slater's proposition made 

 on X -^I interchange may be the answer. As soon as a transformation of 

 O-R potential into another form of energy has occurred, then the 

 exchange can occur across the O-R potentials. The phosphate can thus 

 exchange, and it does not matter at what potential level. We have to 

 consider that very seriously. 



