MITOCHONDRIAL STRUCTURE AND IUN<:TI()N 99 



TaHI.I- 8. Pl«)PlRTli:S OK Q LIPOPROTtIN 



/) Soluble in H2O 



2) Lipid 96%, 4% protein 



S) Homogeneous in ultracentrituge and electrophoresis 



4) Molecular weight about 5 X 10" 



5) Binds cytochrome c, vitamins A, E, and Ki, indophenol, coenzyme Q and phenazine 



6) Accounts for bulk of mitochondrial lipid, coenzyme Q and carotenoids 



7) Denatured by successive freezing and thawing 



8) Disaggregated by cholate and dcoxycholate 



My colleagues, J. Jarnefelt, R. Basford and Howard Tisdale, and I (22, 2) have 

 isolated a lipoprotein from the electron transport particle which has the properties 

 summarized in table 8 and which has been called the Q lipoprotein. There 

 are many fascinating properties of this lipoprotein which I should like to discuss 

 with you, but I shall have to restrict myself to one particular property which is 

 germane to our previous discussion. This lipoprotein contains coenzyme Q in 

 sufficiently high concentration that the possibility cannot be excluded that the 

 bulk, if not all, of the coenzyme Q of the electron transport particle is concen- 

 trated in the lipoprotein. Whatever uncertainty there is as to how much of the 

 total coenzyme Q is concentrated in this lipoprotein, there are no reasons to 

 doubt that a part at least of coenzyme Q normally resides within the lipid core of 

 the lipoprotein and there undergoes cyclical oxidation and reduction. My col- 

 league, Y. Hatefi, has recently shown that the oxidation of reduced coenzyme Q 

 by molecular oxygen catalyzed by a purified cytochrome oxidase preparation 

 (table q) requires, in addition to cytochrome c, the Q lipoprotein (18). This is a 

 most significant series of observations because it demonstrates that the lipoprotein 

 is essential for the catalytic effect of coenzyme Q and it provides the clearest evidence 

 for the concept of small inolecules operating in a shuttle capacity within lipo- 

 proteins. What is still indeterminate is exactly which pair of oxidation-reduction 

 components is linked through coenzyme Q. 



Cytochrome c was one of the first oxidation-reduction components of the elec- 

 tron transfer chain to be isolated. Keilin in the late 1920's succeeded in isolating 



Table 9. Requirement for lipoprotein in oxidation of reduced coenzyme q by 



cytochrome oxidase system 



m/iM RED. CO Q * m//M RED. CO * 



Complete system 97 



No lipoprotein (207 protein) 6 



No cytochrome c (1.5 in/iuioles) 5 



No cytochrome oxidase (0.5 mg) 



Cytochrome oxidase is a purified jireparation which contains a heme. The externally added 

 coenzyme Q in this experiment represents > 50 times the coenzyme Q content of the added 

 lipoprotein. Reaction mixture contains 170 m^moles reduced coenzyme Q in a final volume of 

 I ml. 



* Oxidized/45 sec. at 38°C. 



