Figure 4.

NADH is oxidized superstoichiometrically in aerobic quinone-containing solutions. Complex I was incubated in the presence of ∼50 μM Q (dotted lines) in varying concentrations of NADH (from 0 to 200 μM). The NADH concentrations were measured at 2 min intervals, and the amount of NADH oxidized was determined by comparing measured and initial NADH concentrations. (A) NADH oxidation by 50 μM Q₁ in an aerobic solution in the presence or absence of rotenone (Rot.) and/or asolectin (Aso.). NADH is oxidized superstoichiometrically. (B) An experiment equivalent to that conducted for panel A but in an anaerobic solution (the symbols are conserved). NADH is not oxidized superstoichiometrically. (C) NADH oxidation by 50 μM DQ in the presence of asolectin, in anaerobic (○) and aerobic (●) solutions. NADH is not oxidized superstoichiometrically. (D) NADH oxidation by 50 μM Q₁, IDE, and Q₀ in an aerobic solution in the presence of rotenone and asolectin. NADH is oxidized superstoichiometrically. Conditions: 20 mM Tris-HCl, pH 7.55, 32 °C, 2.3 μM rotenone, 0.4 mg/mL asolectin.