The inhibition of plant mitochondrial respiration by the synthetic analog of ubiquinone, 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT).

The quinone analog, 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT), has been shown to inhibit cyanide-sensitive and cyanide-insensitive respiration in higher plant mitochondria. The inhibition is dependent upon the concentration of mitochondrial protein. The low concentrations of UHDBT required to inhibit the cyanide-sensitive pathway (microM) and the cyanide-insensitive pathway (nM) indicate that UHDBT is acting as a tight-binding inhibitor of ubiquinol oxidation. Inhibition of both pathways was dependent upon pH. It is shown that UHDBT appears to be a less potent inhibitor of cyanide-sensitive NADH oxidation than of cyanide-sensitive succinate oxidation, and that the pH dependence of inhibition of these two pathways differs. The inhibition of NADH and succinate oxidation by the cyanide-insensitive pathway shows similar pH dependences although at a given pH NADH oxidation is more susceptible to inhibition than succinate oxidation.