Fungal quinone pigments as oxidizers and inhibitors of mitochondrial NADH:ubiquinone reductase

Abstract

The interaction of fungal quinone pigments bostricoidin, fusarubin, javanicin, and 2-oxyjuglone with mitochondrial NADH:ubiquinone reductase (complex I, EC 1.6.99.3) has been studied. The bimolecular rate constants (turnover number ( TN) K m ) of rotenone-insensitive reduction of these compounds are in the range of 1.2 × 10 4–1.6 × 10 5 m −1s −1. 2-Oxyjuglone acts as inhibitor of NADH:ferricyanide reductase reaction of complex I ( K I = 30 μM). All quinone pigments, except javanicin, decrease the TN of reduction of 5,8-dioxy-1,4-naphtoquinone being reduced at its binding site but with significantly lower TN. They do not affect the rotenone-sensitive reduction of ubiquinone-1. The binding of quinone pigments close to the NADH and ferricyanide binding site is suggested. It seems that quinone pigments, especially 2-oxyjuglone, react with complex I faster than it follows from their approximate values of one-electron reduction potential calculated from their reactivities with flavocychrome b 2 and adrenodoxin.