Cytochrome b in the Respiratory Chain 



COOH 



I 

 C— SE 



CH 



COOH 



+ fpHa ^ 



COOH 



I 

 CH 



II 

 CH 



I 

 COOH 



+ ESH + fp 



589 



(20) 



Sum COOH 



CH2 



I + 26+++ - I2 



CH2 



COOH 



COOH 



I 

 CH 



II 

 CH 



I 

 COOH 



+ 26++ - I2 + 2H^ 



(It should be understood that fp and ESH are part of the same protein.) 



Since there are no labile 'energy-rich' intermediates which would be subjected 



to hydrolysis in the non-phosphorylating preparations, the reduction of 



cytochrome b by succinate would also proceed rapidly in these preparations. 



It is possible that cyanide reacts with 6+++ — I2 to give a product which can 



be oxidized back to 6^ 



l2+by 



but whose iron atom cannot be 



reduced to ferrous. The oxidation can then proceed only by electron transfer 

 through the I2 part of the 6^^+ — I2+, following a path analogous to the non- 

 phosphorylating pathway for DPNH, thus 



COOH 



I 

 CH2 



CHa 



I 

 COOH 



+ fp + ESH 



COOH 



I 

 HC— SE 



I 

 CH2 



I 

 COOH 



+ fpH2 



(17) 



fpH2 + 6+++ - I2+ ^ 6+++ - I2 + fpH + H+ 



fpH + q+++ ^ fp + c^^ + H+ 



6+^-^ - I2 + CN- ^ 6+++ - I2 - CN- 



Ci++ + C+++ ^ Ci+++ + C++ 



L - CN- + c^ 



6+++ - I2+ + CN- + c^ 



(21) 



(22) 



(23) 



(11) 

 (24) 



