(3) flavin •2H + 2cytochrome c(Fe+++) 



^ - 2f 



reductase 



+ 2e 



283 



flavin + 2cytochrome c (Fe++) + 2H+ 



(4) 2cytochrome c (Fe++) + 2H+ + IO2 



oxidase 



- 2e 



2cytochrome c (Fe+++) + H2O 



(1) + (2) 

 + (3) + (4) 



RH2 



Substrate 

 (reduced) 



+ \0, 



2e 



H2O + R 



Substrate 

 (oxidized) 



It will be observed that the net result of the oxidation of the substrate 

 to product is the removal of two hydrogen atoms [two hydrogen ions 

 plus two electrons, since H (atom) = H+ (ion) + e (electron)] from the 

 substrate, which combine with oxygen to form water. It should also be 

 noted that the coenzyme that becomes reduced in one reaction is reoxi- 

 dizcd in the next and thus is ready for the first reaction again; this is 

 indicated by the broken arrows in the scheme. 



In subsequent chapters (13, 16), it will be explained that the degrada- 

 tion of foods is a stepwise process which proceeds through a series of inter- 

 mediary compounds before the end products are excreted by the organism. 

 The above scheme suggests that this situation also applies to oxidation- 

 reduction processes. It should be realized, furthermore, that a certain 

 increment of energy becomes available at each of the steps of the oxida- 

 tion-reduction chain and that this energy can be transferred to functions 

 useful to the organism by appropriate, stepwise mechanisms, such as 

 the formation of high energy phosphate linkages (Chap. 16). 



Although some tissues contain all the electron transferring systems 

 indicated in the scheme, it should be remembered that not all of the 

 steps are necessary for every process. For example, the oxidation-reduc- 



