134 BRITTON CHANCE 



(2) that the cytochrome should be in a reduced state blocked from the 

 oxidizing power of molecular oxygen either by anaerobiosis or by a suitable 

 inhibitor of cytochrome oxidase; (3) that the respiratory chain must 

 initially contain both oxidized and reduced components, since for every 

 oxidation there must be a reduction. Succinate-linked pyridine nucleotide 

 can be used as the acceptor of the reducing equivalents from cytochromes 

 from other parts of the chain. Under these conditions the efficiency of the 

 ATP-electron transfer reaction is high, the ATP/f value being 3 or less. 

 Thermodynamically the phosphate potential required for cytochrome 

 oxidation suggests that ATP can interact with redox couples of the 

 respiratory chain as individuals without supplying a phosphate potential 

 corresponding to the complete span from pyridine nucleotide to cyto- 

 chrome oxidase. 



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