478 5. QUINONES 



pared to mitochondria from normal livers (Martins and Nitz-Litzow, 

 1954 a), and the addition of vitamin K^ to the mitochondria restores the 

 P:0 ratio to near-normal levels (Martins and Nitz-Litzow, 1954 b), leading 

 to the postulate that vitamin K^ is in some manner involved in phosphoryl- 

 ation. Menadione is inactive in this system but both it and phthiocol are 

 able to augment markedly photosynthetic phosphorylation in chloroplasts 

 (Arnon et al., 1955). Additional evidence is provided by the uncoupling 

 action of Dicumarol, a vitamin K antagonist. Phosphorylation accompanying 

 the oxidation of hydroquinones has been demonstrated in many systems, 

 and a few examples will be mentioned. Menadiol is oxidized by an enzyme 

 preparation from Azotobacter vinelandii and this is associated with the for- 

 mation of some ATP, although the P:0 ratio is low (Schils et al., 1960). 

 Mitochondria similarly oxidize QgH-P with the generation of ATP, this 

 being sensitive to antimycin A and 2,4-dinitrophenol, and it is likely that 

 the ubiquinones participate directly in phosphorylation during electron 

 transport (Gruber et al., 1963). The phosphorylation occurring during the 

 oxidation of 3-methylmenadiol-P by mitochondria seems to involve the 

 phosphorylated semiquinone intermediate, which was detected by electron- 

 spin resonance (Bond and Mason, 1962). Oxidative phosphorylation by 

 mycobacterial preparations is lost following ultraviolet irradiation, and 

 this may be restored by vitamin K^ (Brodie and Ballantine, 1960). Certain 

 other naphthoquinones can restore electron transport but not phosphoryla- 

 tion. More indirect evidence suggests that a-tocopherylquinone may also 

 participate in phosphorylations. 



Various mechanisms have been proposed and most involve a phosphoryl- 

 ated hydroquinone intermediate; several reviews are available (Harrison, 

 1958; Brodie, 1961, 1964; Todd, 1960; Clark and Todd, 1960). The exact 

 reactions whereby the phosphorylated intermediate is formed have not 



CH3 

 H3C' "CHr+CHj— CH=C— CH, 



Ubichromenol 



[J-H 



— 'a 



been completely estabhshed, but Brodie (1964) since 1961 has accumulated 

 much evidence that 6-chromanol derivatives are formed from both ubi- 

 quinones and vitamin K^ by cyclization involving the y-position of the 

 side chain. Saturation of the phytyl side chain of vitamin K^ to give 2,3- 

 dihydrophytyl- vitamin K^ not only abolishes the ability to restore phospho- 



