Redox cycling of beta-lapachone and related o-naphthoquinones in the presence of dihydrolipoamide and oxygen.
Lipophilic o-naphthoquinones (beta-lapachone, CG 8-935, CG 9-442, CG 10-248, and mansonones A, C, E, and F), catalyze the oxidation of dihydrolipoamide (DHLA) by oxygen, whereas p-naphthoquinones (alpha-lapachone and menadione) are scarcely active. The greatest effects corresponded to beta-lapachone and its analogues. Quinol production was demonstrated by (a) the absorption spectrum of the reduced quinone, and (b) the effect of pH variation on the rate of quinone-catalyzed DHLA oxidation. Superoxide dismutase (SOD) inhibited the rate of cytochrome c reduction and decreased the apparent rate of oxygen consumption by several DHLA/o-naphthoquinone systems. SOD also inhibited the rate of quinol oxidation by oxygen, after quinone reduction by a stoichiometric amount of DHLA. Catalase enhanced the effect of SOD, but in its absence catalase was inactive. It is concluded that quinone-catalyzed oxidation of DHLA implies a free-radical mechanism in which the quinol and superoxide radicals play an essential role.
Molina Portela
M P
MP
Bioenergetics Research Centre, School of Medicine, University of Buenos Aires, Argentina.
Stoppani
A O
AO
D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000737:chemistry; D009285:Naphthoquinones / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D013482:Superoxide Dismutase / Q000737:chemistry; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000737:chemistry
D006873:Hydroquinones; D009285:Naphthoquinones; C007409:dihydrolipoamide; C014638:beta-lapachone; D008063:Thioctic Acid; D013482:Superoxide Dismutase; D010100:Oxygen