BRIXTON CHANGE 



spiratory chain that is proposed for cellular respiration should be 

 examined critically in view of these data. 



It is interesting to note that the oxidation of cytochrome c 

 relative to cytochrome a is faster in the nonphosphorylating 

 preparation than in the phosphorylating one. And the reverse 

 is true of cytochrome h. It is very likely that not only can the 

 reactivity of components in the respiratory chain be decreased 

 upon the loss of oxidative phosphorylation (e.g., cytochrome h), 

 but some may also increase. 



RESPIRATORY CHAIN 



On the basis of substrate-inhibitor techniques and rapid 

 reaction methods, the respiratory chain of intact mitochondria, 

 whole ascites tumor cells, and baker's yeast are observed to con- 

 tain the sequence of six spectroscopically identifiable compo- 

 nents : cytochromes a^,a, c, and b, flavoprotein, and DPNH. Other 

 components which cannot be adequately identified and charac- 

 terized are omitted from the present discussion (Slater's factor, 

 cytochrome Ci, peroxidase complex II, etc.). If one includes the 

 data obtained on the basis of the ADP action spectrum described 

 above, at least three sites of oxidative phosphorylation should be 

 included in the chain, at cytochromes c, b, and DPNH. Other 

 data indicate phosphorylation between cytochrome c and 

 oxygen as well (50,54). According to the mechanism proposed, 

 these phosphorylation reactions affect the intact respiratory 

 chain as follows : * 



02 



h 



ki ki ill k\i 



-* fp -»■ DPN -► acetoacetate (19) 



*i ki kh k7 kt kii kit 



O2 *- 03" ♦- a" ^ c" ♦_ b" -_ rfp *_ DPNH*- /3 hydroxybutyrate (20) 



X, Pi 



ADP 



V 

 c" 



X, Pi 

 ADP 



• I A"~I 



X, Pi 

 ADP 



DPNH 



* BOHB = /3 hydroxybutyrate, fp = flavoprotein, rfp = reduced 

 flavoproteins. Cytochromes are designated by letter only. 



332 



