Lucigenin is a mediator of cytochrome C reduction but not of superoxide production.
The relevance of lucigenin (bis-N-methylacridinium nitrate)-amplified chemiluminescence (CL) as a specific assay for superoxide ion has recently been disputed (S. I. Liochev and I. Fridovich, Arch. Biochem. Biophys. 337, 115-120, 1997). These authors suggested that the redox cycling of lucigenin can lead to the formation of additional amount of superoxide ion. However, thermodynamic consideration shows that the equilibrium for the reaction O*-2 + Luc2+ if O2 + Luc*+ is completely shifted to the right (Keq = 10(6)); therefore, the redox cycling of lucigenin is of no importance. This conclusion is supported by the study of the effects of lucigenin on cytochrome c reduction by xanthine oxidase. It was found that lucigenin did enhance the rate of cytochrome c reduction with xanthine as a substrate, but it did not increase the rate of xanthine oxidation. When NADH was used as a substrate, lucigenin inhibited the SOD-dependent component of cytochrome c reduction and enhanced both the SOD-independent cytochrome c reduction and NADH oxidation, being a sole acceptor of an electron from the enzyme. All these findings indicate the extremely low probability of lucigenin redox cycling. In our opinion, lucigenin-amplified CL remains the most sensitive and highly specific test for superoxide formation in biological systems.
Afanas'ev
I B
IB
Vitamin Research Institute, Nauchny pr. 14A, Moscow, 117820, Russia. iafan@aha.ru
Ostrachovitch
E A
EA
Korkina
L G
LG
D000166:Acridines / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008163:Luminescent Measurements; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism*; D019820:Xanthine / Q000378:metabolism; D014969:Xanthine Oxidase / Q000378:metabolism
D000166:Acridines; D003574:Cytochrome c Group; D009243:NAD; D013481:Superoxides; D019820:Xanthine; C033472:10,10'-dimethyl-9,9'-biacridinium; D014969:Xanthine Oxidase