The mitochondrion in bloodstream forms of Trypanosoma brucei is energized by the electrogenic pumping of protons catalysed by the F 1 F 0 ‐ATPase

Bloodstream forms of Trypanosoma brucei were found to maintain a significant membrane potential across their mitochondrial inner membrane (ΔΨm) in addition to a plasma membrane potential (ΔΨp). Significantly, the ΔΨm was selectively abolished by low concentrations of specific inhibitors of the F 1 F 0 ‐ATPase, such as oligomycin, whereas inhibition of mitochondrial respiration with salicylhydroxamic acid was without effect. Thus, the mitochondrial membrane potential is generated and maintained exclusively by the electrogenic translocation of H + , catalysed by the mitochondrial F 1 F 0 ‐ATPase at the expense of ATP rather than by the mitochondrial electron‐transport chain present in T. brucei . Consequently, bloodstream forms of T. brucei cannot engage in oxidative phosphorylation. The mitochondrial membrane potential generated by the mitochondrial F 1 F 0 ‐ATPase in intact trypanosomes was calculated after solving the two‐compartment problem for the uptake of the lipophilic cation, methyltriphenylphosphonium (MePh 3 P + ) and was shown to have a value of approximately 150mV. When the value for the ΔΨm is combined with that for the mitochondrial pH gradient (Nolan and Voorheis, 1990), the mitochondrial proton‐motive force was calculated to be greater than 190 mV. It seems likely that this mitochondrial proton‐motive force serves a role in the directional transport of ions and metabolites across the promitochondrial inner membrane during the bloodstream stage of the life cycle, as well as promoting the import of nuclear‐encoded protein into the promitochondrion during the transformation of bloodstream forms into the next stage of the life cycle of T. brucei.