Discussion 203 



but separated from each other; and also three different kinds of vitamin 

 K derivatives with three different potentials. This scheme, of course, is 

 all manufactured out of whole cloth, right here on the spot, and I don't 

 really believe it. I just want to account for the fact that dicoumarol 

 uncouples at all three phosphorylation sites. 



It seems to me that there is a very important discrepancy between 

 this fact and Prof. Martins' views. 



Krebs: Prof. Martins (1956, Iji Proc III int. Congr. Biochem., p. 1. 

 New York: Academic Press) left out the flavoprotein in his earlier 

 schemes, when he introduced vitamin K. Is he ready to put it back 

 again, having discovered that the vitamin K reductase is a flavoprotein? 

 There ought to be room for both in the series. 



Martius : Four years ago, we believed that vitamin K reductase was 

 not a flavoprotein, but now we know that it is a flavoprotein. Now we 

 have at least two flavoproteins in the respiratory chain. 



Krebs: It has always been understood that flavoprotein is a generic 

 name; there may be several which may react in series. 



Slater: Prof. Potter's point as to whether reduced vitamin Kj was 

 oxidized again fast enough to account for it being in the main chain 

 interested us very much. We tried to investigate that but could only 

 use reduced vitamin Kg as a model, and that was very rapidly oxidized, 

 getting right into the respiratory chain. We could not use reduced 

 vitamin Kj, because we did not know how to make it at the time. Does 

 your answer to Prof. Potter's question mean that reduced vitamin Kj 

 can be oxidized by oxygen with a mitochondrial preparation? 



Martius: The answer is the same as to Prof. Potter's question. We 

 were able to demonstrate the rapid oxidation of reduced vitamin Kj by 

 cytochrome b (cytochrome b preparation of Stotz) with exclusion of 

 oxygen. 



Slater : What is the final hydrogen acceptor — oxygen or cytochrome 6? 

 Martius: Cytochrome b. 



Lipmann: I was always rather impressed by the naphthoquinone 

 possibility. The problem of a converter mechanism of electron potential 

 and phosphate potential was raised quite a while ago (Lipmann, F. 

 (1946). In Currents of Biochemical Research, p. 137. Ed. Green, D. E. 

 New York : Interscience Publishers). If we want to bring some reason 

 into the oxidative phosphorylation, we have to keep in mind that we 

 need such converter mechanisms. We need the mechanism which 

 converts electron potential into phosphate bond potential. I still hope 

 that vitamin K will somehow fit in. I cannot quite see how it can fit 

 only into one place : perhaps quinones are on several places and perhaps 

 dicoumarol would inhibit them all. 



King : If reduced K^ can be oxidized t)y cytochrome c, why do you put 

 b and x into the chain, especially if the system is not antimycin-sensitive? 

 Secondly, is your cytochrome c reductase the same as Mahler's? 



Martius : It is true that reduced vitamin K^ can react with cytochrome 

 c. In that case, however, we could expect a maximal P/O ratio in 

 mitochondria of only 2. Our vitamin K reductase is not identical with 

 Mahler's cytochrome c reductase. 



