Fig. 2.

Determination of 2-heptyl-4-hydroxyquinoline- N-oxide (HQNO) IC₅₀ for wild-type and I379E NDH-2 variants at two menadione (MD) concentrations. A) and B) HQNO inhibition curves for WT NDH-2 in the presence of 400 and 50 μM MD, respectively. C) and D) HQNO inhibition curves for the I379E NDH-2 mutant in the presence of 400 and 50 μM MD, respectively. Concentration of NADH was set at 200 μM for all experiments. The error bars, which represent 95% confidence intervals, are for triplicate activity assays at each HQNO concentration. A variable slope model was fitted to determine the IC₅₀ values. In each panel, NADH:MD oxidoreduction activities in the absence of HQNO are used for 100% and are A) 959.3, B) 562.5, C) 273.4 and D) 82.4 s⁻¹, respectively.