98 SUBCELLULAR PARTICLES 



My colleague, F. L. Crane, discovered in mitochondria a fat-soluble quinone 

 which was capable of undergoing oxidation and reduction in the electron transfer 

 chain. This discovery was the starting point for an extensive series of studies by 

 R. Lester, Y. Hatch and F. L. Crane on the chemistry (23) and enzymatic (12, 

 20, 17) function of this new quinone, which has been named coenzyme Q. Some 

 of the pertinent chemical and enzymatic properties of coenzyme Q or Q075, as it 

 was first called, are summarized in tables 6 and 7. 



The definitive structure of coenzyme Q was established first by Karl Folkers 

 and his group at the Merck Sharpe and Dohme Research Laboratories (32a), 

 and this was later confirmed by R. A. Morton of Liverpool in collaboration with 

 a group of the Hoftmann-La Roche Company in Basel (27a). The formula shown 

 below represents the structure of the coenzyme present in higher animals, viz., 

 coenzyme Qio- 



O 



CH3O 

 CH,0 



CH3 CH3 



I 

 [CH,CH = C-CH.]ioH 



O 



Bacteria and microorganisms contain variants with 6, 7, 8 and 9 isoprenoid units 

 in the side chain, and these are called coenzyme Qe, coenzyme Q7, etc. (23). 



The available evidence points to the position of coenzyme Q in the electron 

 transfer chain between cytochrome b on the electron donor side and cytochrome 

 a on the electron acceptor side. Whether coenzyme Q accepts electrons from 

 reduced cytochrome b is unknown. But it can be stated unambiguously that 

 reduced coenzyme Q does not donate electrons directly to cytochrome a. 



Table 6. Chemical profile of coenzyme q 

 /) Orange yellow crystals, m.p. 49.9° 



2) CssHssOl 



^) Molecular weight 850 



4) Ultraviolet and infrared confirm quinone structure 



5) Quinone ring system — side chain with approximately 10 isoprenoid units 



6) Isolated from mitochondria and particles with electron transport activity 



7) Analogs of coenzyme Q are widely distributed in all aerobic organisms 



Table 7. Evidence for role of coenzyme q in electron transport 



/) > Respiratory rate of tissue > concentration {Azotohacter > heart > liver) 



2) Internal coenzyme Q reducible by succinate and DPNH in ETP and mitochondria 



j) Restores succinoxidase activity of heptane-extracted particles 



4) Phosphate freezes coenzyme Q in reduced form, ADP in oxidized form 



5) Oxidoreduction of coenzyme Q inhibited by antimycin and other respiratory inhibitors 



