78 E. C. Slater and W. C. Hulsmann 



phosphorylating mitochondria and upon which the reaction 

 depends to overcome the thermodynamic difficulties". 



The finding (Purvis, 1958) that succinate does not reduce 

 DPN, but instead causes the accumulation of DPN ^^ I can 

 be explained, without suggesting a reversal of the respiratory 

 chain, by assuming that either X /-^ Ig or X '^ I3 formed in 

 reactions (1) and (2), with succinate as substrate, can react 

 with Ij [possibly via X '--' P (see Purvis, 1958)], e.g. 



[reactions (1) and (2)] 



X + I2 > X ^ I2 (13) 



X -- I2 + Ii ^ X ^ Ii + I2 (14) 



X -- Ii + DPN ^ DPN ^ Ii + X (15) 



[reactions (1) and (2)] 



Sum reaction DPN + I^ > DPN ^ I^ 



In other words, the energy-conservation reactions linked with 

 the oxidation of succinate are used to synthesize the energy- 

 rich compound DPN '^ I^ from its constituents. 



This explanation also takes account of the inhibition by 

 antimycin of the reduction of DPN by succinate (Chance and 

 Hollunger, 1957), since antimycin inhibits reaction (13), and 

 the inhibition by amytal, if the latter inhibits reaction (15). 

 The inhibition by DNP (Chance and Hollunger, 1957) is also 

 easily explained, since it promotes the hydrolysis of X /^ I2 

 and X /^ Ij. 



Importance, in vivo, of the control of respiratory rate 

 by processes related to oxidative phosphorylation 



Equations (l)-(Sb) predict that, in the absence of reactions 

 liberating I from one of its bound forms, reaction between 

 AH2 and B is inhibited, and that this inhibition would be 

 relieved by the addition of ADP and inorganic phosphate. 

 Chance and Wilhams (1956) showed that addition of ADP to 

 liver mitochondria relieved the inhibition of respiration and 

 caused the oxidation of all components of the respiratory 



