MITOCHONDRIAL LIPIDS AND THEIR FUNCTIONS IN THE RESPIRATORY CHAIN 1 87 



Experiments with antimycin A, which inhibits oxidation of ubiquinol, 

 have shown that the enzymically reducible ubiquinone is only 80-90*;' o of 

 the total. Thus succinate in State 4 is actually giving complete reduction 



Oi2r 



260 280 300 



Wavelength (m//) 



Fig. I. Steady-state oxidation-reduction levels of ubiquinone in rat-liver 

 mitochondria. 



— ^_^ — total ubiquinone (oxidized); 



— □ — total ubiquinone reduced with XaBHj; 



— X— Pi-hair; — A— Pj + ADP + air; 



— O — Pi + succinate -I- air; — • — Pj + succinate -I- ADP + air. 



of the enzvmicallv active material, while /S-hydroxybutyrate in State 4 is 

 giving about 80",, reduction. 



These changes are qualitivelv similar to those reported by Chance [21] 

 for guinea-pig kidnev mitochondria and support the view that the oxida- 

 tion of ubiquinol is blocked in the absence of a phosphate acceptor by an 

 inhibitorv interaction which could involve energy conservation as a high- 

 energv intermediate UQIL^I bv a series of reactions as follows: 



UQ + I - UQ.I (i) 



UQ . I + FPH., = UQH.. - I + FP (2) 



UQH.,^I^X =UQH., + I-X (3) 



I~X + ADP + P, -X+I + ATP (4) 



