Fig 5. TbIF1 functions as a unidirectional inhibitor of T. brucei F_oF₁-ATP synthase.

(A) Total ATPase activity was measured in TbIF1 OE cells that were noninduced (grey) or induced for 2 days with tet (grey cross-hatch). To define the contribution of F_oF₁-ATPase to the total ATPase activity measured, samples were also incubated with either azide (AZ, 1 mM) or oligomycin (OM, 2.5 μg/ml). The total amount of free-phosphate detected in the untreated noninduced sample was set at 100%. (means ± s.d.; n = 3; ** p < 0.001; Student’s t test). (B) The amount of ATP synthesized by oxidative phosphorylation was measured in the digitonin-extracted mitochondria from both noninduced (NON) TbIF1 OE cells and cells induced for 2 days (IND2). The reaction was started by the addition of succinate and ADP. Malonate (mal.) and atractyloside (atract.) were added as specific inhibitors of succinate dehydrogenase and the ATP/ADP carrier, respectively.