Energy Transfer and Consenalion in the Respiratory Chain 607 



cytochrome c. On the basis of these data and those of a further experiment 

 represented in Fig. 4, we feel that arguments in favour of considering cyto- 

 chrome q as a fully active member of the respiratory chain are somewhat 



steady-state 



I I ' I I I I I ' ' ' I -> 

 500 550 600 



A(m;j) 



Fig. 3. A low temperature steady-state spectrum representing the difference in 

 absorbancy between the oxidized beef heart mitochondria and the steady-state 

 reduced beef heart mitochondria at temperatures of liquid nitrogen (77°K). The 

 percentage reduction of the components is indicated on the figure. Succinate as 

 substrate (Expt. 966a). 



500 



Fig. 4. A low temperature spectrum representing the difference in the steady-state 

 oxidation level of mitochondria in state 4 and those in state 3 due to treatment 

 with 100 /«M dibromophenol. Rat liver mitochondria suspended in sucrose 

 phosphate medium treated with 4 mw glutamate and 200 /<M azide. One of the 

 samples is treated with 100 /tM DBP. Cytochrome b is oxidized, cytochromes c 

 and Cj are reduced (Expt. 952b). 



strengthened. Ultimately, kinetic studies of this component would be highly 

 desirable. 



It is apparent that these approaches are the most suitable for providing 

 direct evidence for the participation in electron transfer of pigments associated 

 with the respiratory chain. Those components on which adequate data are 



