Maesaquinone: a novel inhibitor of plant mitochondrial respiratory enzymes that react with ubiquinone.

The effect of maesaquinone, 2-(14-nonadecenyl)-3,6-dihydroxy-5-methyl-1,4-benzoquinone, on plant mitochondrial respiration has been investigated. In mitochondria isolated from thermogenic Arum maculatum spadices, this compound inhibits both cytochrome and alternative pathway activities. Kinetic analyses reveal that this inhibition is the result of potent effects of maesaquinone on the alternative oxidase (ID50 < 0.3 microM) and complex III (ID50 < 5 microM). Succinate dehydrogenase and external NADH dehydrogenase are also inhibited, albeit to a lesser extent (approximately 30% at 1 microM). These data suggest that maesaquinone specifically affects the interaction of the respective enzymes with ubiquinone.