GENERAL PRINCIPLES OF BIOCHEMICAL ENERGETICS 



141 



In Table XII is listed a series of Eo values for a number of systems 

 important biochemically. If system A is characterized by a higher (or 

 less negative) value of E than system 5, then B can serve as a reducing 

 system for system A, and A as an oxidizing system for B. 



We have seen (p. 134) that there is a definite relation between the change 

 in free energy AF and electromotive force E, and that by means of the 

 following equation it is possible to calculate the electrical work accompany- 

 ing the formation of a mole of reaction-product. 



AF 



■nFE 



Let us now consider, inside a cell, the oxidation (or dehydrogenation) 

 of lactate to pyruvate, the proton and the electron of the hydrogen, or the 

 electron alone, being conducted through several intermediates as far as 

 cytochrome-c. Let us also suppose that the pyruvate and lactate are 

 present at equal concentrations and that the cytochrome-c is 50% reduced 

 and 50% oxidized. The number of intermediates does not matter. E' o 

 for the lactate-pyruvate system = 0-180 at pH 7-0; at the same pH, for 

 the system cytochrome-c (Ox)/cytochrome-c (Red), E' o = 0-262. Since 

 both systems are 50% reduced, E = E' o for both, 



and zl5 = 0-442 volts 

 whence -AF =2x 96,500 x 0-442 = 85,500 J = 20,500 cal. 



So that the energy liberated by the oxidation of a mole of lactate by a 

 mole of cytochrome-c under the specified conditions is 20,500 calories. 

 Johnson calculates that this amount of energy would be sufficient to keep a 

 100 W lamp alight for 14 min. 



Table XII 

 Some oxidation-reduction potentials 



