204 Discussion 



Siekevitz : Prof. Lehninger, did you have in mind with the parasitic re- 

 lationship that perhaps K^ does not act as an O-R compound, but that 

 it may be one of the X's? 



Lehninger: Prof. Potter's statement about the requirements of what 

 constitutes a chain does not necessarily exclude the enzyme described 

 by Prof. Martins as such a "parasite". Perhaps it is the oxidation/ 

 reduction state of the naphthoquinone, as Prof. Lipmann has just 

 mentioned, that conditions the effectiveness of X, Y and Z to participate 

 in phosphorylation. We have presented evidence elsewhere that the 

 oxidation /reduction state of the respiratory chain and/or other things 

 associated with that chain, condition the rate of the '^P exchange and 

 ATPase activity (Wadkins, C. L., and Lehninger, A. L. (1957). J. Amer. 

 chem. Soc, 79, 1010; 1959, J. biol. Chem., in press). I do not think that 

 your point excludes such a parasitic relationship. Prof. Martins' 

 enzyme may be one of these that happens to fit at the level of cyto- 

 chrome h or c. There may also be some other enzymes which happen to 

 fit further along the chain — that is pure speculation. 



Slater : We are toying with the idea that vitamin E is one of the X's 

 or the I's. I do not see where you fit in the phylloquinone reductase in 

 this scheme if you make vitamin K an X or an I. 



Siekevitz: Could it not be that vitamin K^ acts as an X only; and 

 whether it is oxidized or reduced is determined by its reductase and thus 

 the reductase would determine its effectiveness in phosphorylation? 



Slater : This discussion turns now on the experimental results : whether 

 the state of oxidation-reduction in the respiratory chain does or does 

 not have an influence on the reaction. 



