Discussion 201 



Siekevitz : It could also be that in all the phosphorylation steps every- 

 thing will funnel into one X compound, and the all-or-none effect could 

 be accounted for in this manner. 



Lipmann: Prof. Lehninger has shown that there are different ways of 

 uncoupling, and they all seem to be all-or-none. Then one cannot 

 think of it funnelling into one step but rather into two steps. 



Estabrook : If the vitamin K reductase is not inhibited by p-chloro- 

 mercuribenzoate, do you get oxygen consumption in the presence of 

 p-chloromercuribenzoate during phosphorylation? If the by-path is 

 blocked, then all the electrons would be funnelled to the vitamin K 

 reductase, using DPNH as substrate. 



Martins : As yet we have not done this experiment. There are many 

 enzymes which could be blocked by p-chloromercuribenzoate. 



Lipmann : Does DNP inhibit the reductase? 



Martins: No, it does not. 



Chance: I was interested in the system which Prof. Martins has 

 discussed and which we represent as follows : 



ADP 



I 

 K > cytochrome b 



dicoumarol 

 (~5 X 10-6 m) 



reductase 

 (non-phosphorylating) 



We have an opportunity to test more critically the hypothesis presented 

 and to see whether the site of dicoumarol action would be specific at 

 the point indicated. While both dicoumarol and ADP separately acceler- 

 ate the flow of electrons through this system. Prof. Martins' hypothesis 

 would require that a block with dicoumarol would activate the non- 

 phosphorylating reductase pathway. We compared the effect of 

 dicoumarol and ADP on phosphorylating liver mitochondria. If 

 dicoumarol blocks at the point indicated, it would cause a diminution 

 of the flow of electrons to cytochrome b. The steady state oxidation- 

 reduction level of cytochrome b would then go considerably more 

 oxidized, but that of cytochrome c would stay about the same. In the 

 presence of dicoumarol (5 x 10-^ m) the bands of both cytochromes b 

 and c show approximately the same changes (Fig. 14, p. 109). Further- 

 more, the electron flow was not blocked between "fp" and "b". It 

 appears that dicoumarol has no selective action on the possible site of 

 the "K reductase" or K itself. Thus, the proposed sequence is not 

 supported by this particular experimental test. 



Potter: I wonder whether, at a dicoumarol concentration as low as 



