HENRY R. MAHLER 



Interaction between Flavoprotein and Cytochromes 



We might then summarize and extend the possible means 

 of interaction between enzymes at the flavoprotein and those at 

 the cytochrome level in the following manner (see Figure 3). 

 Probably the most significant feature of this scheme is its inherent 

 complexity. Instead of one straight-line path from substrate to 

 oxygen we find the electrons traveling several paths in parallel. 



|i ^CYTOCHROMES b'' | l 'CYTOCHROME OXIDASg* \ 

 OF 



f 



Figure 3. 



This is not to suggest that all paths will be operative at any one 

 time. During any one set of physiological parameters probably 

 only one of the several alternatives will actually be in use. The 

 switches are set for this particular alternative. But the other 

 possibilities are always present. Under the influence of metabolic 

 controls at one or several junction points an alternate path may 

 become obligatory. Thus the electrons may be diverted from say 

 a relatively slow but energetically efficient to a more rapid but 

 ineflficient route, for example, during uncoupling of oxidative 

 phosphorylation (20). Another feature worth noting may be 

 that quinones (e.g., vitamin K) and cytochrome c lie on parallel 

 paths. The scheme also illustrates a second point: electron 

 transfers from the flavin stage onward, at least in the native 



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