Energy Transfer and Conservation in the Respiratory Chain 609 



the added ADP is phosphorylated and the cytochrome is reoxidized. Addi- 

 tion of 22 [xu dicoumarol then causes a much more abrupt reduction of 

 cytochrome c (0-28 ^moles of Fe 1.-^ sec"^) — almost threefold faster {Note 4). 

 Similar kinetic studies have been made upon phosphate addition to the ADP- 

 treated mitochondria. 

 On the basis of data of this type, equations for the interaction with the 



Aerobic gQuM ADP 550-540m;j . 

 mitochondria l ■^ -^- 



plus succinate-* log lo/I =0.003 



and 

 250;jM Azide 



Cytochrome c reduction \ 

 K 50 sec n 



Fig. 5. A comparison of the kinetics of reduction of cytochrome c caused by ADP 

 or dicoumarol addition. Succinate-treated aerobic rat liver mitochondria in salt 

 medium (containing 0- 1 mPi ; but fluoride-free) treated with 4 mM succinate and 

 250 /zM azide. The additions of ADP and dicoumarol are indicated by the arrows. 

 A downward deflection of the trace corresponds to an increase of absorbancy at 

 550 m/i with reference to 540 m/<. The reaction rate is measured as soon as the 

 stirring artifact has terminated. Temperatvu-e 10°C (Expt. 525b). 



carriers can be written; (we rely upon Plaut's data on the exchange reaction 

 (Plaut, 1957) for the order of Equations 9 and 10). 



DPNH --^ I -H X v- DPNH -|- X -- I (7) 



X ^ I + Die ^ X -1- I -f- Die (8) 



X'-I-l-P^X'-'P-f-I (9) 



X ~ P + ADP ^ ATP -f X (10) 



Slater (1953) used the symbol e to indicate that a ligand other than 

 phosphate interacts with the carriers. Spectroscopic studies of the steady- 

 state oxidation levels of the carriers showed that ADP and Pi reheve an 

 inhibition of the oxidation of reduced pyridine nucleotide in phosphorylating 

 mitochondria (Chance and Williams, 1954), and on the basis of these data 

 interaction of DPNH with an inhibitory hgand, I, in a configuration 

 DPNH '--' I was postulated (ehance and Williams, 1955c). Myers and Slater 

 (1957), in an attempt to avoid multipHcity of nomenclature, used I in place 

 of C. Lehninger, Wadkins, Cooper, Devlin and Gamble (1958) however, do 

 not explicitly indicate inhibitory interactions but instead use the symbol X 

 where Slater (1953) used C. 



