The mitochondrion in bloodstream forms of Trypanosoma brucei is energized by the electrogenic pumping of protons catalysed by the F1F0-ATPase.
Bloodstream forms of Trypanosoma brucei were found to maintain a significant membrane potential across their mitochondrial inner membrane (delta psi m) in addition to a plasma membrane potential (delta psi p). Significantly, the delta psi m was selectively abolished by low concentrations of specific inhibitors of the F1F0-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 F1F0-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 F1F0-ATPase in intact trypanosomes was calculated after solving the two-compartment problem for the uptake of the lipophilic cation, methyltriphenylphosphonium (MePh3P+) and was shown to have a value of approximately 150 mV. When the value for the delta psi m 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.
Nolan
D P
DP
Department of Biochemistry, Trinity College, Dublin, Ireland.
Voorheis
H P
HP
D000818:Animals; D004734:Energy Metabolism; D007425:Intracellular Membranes / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials; D008928:Mitochondria / Q000502:physiology* / Q000648:ultrastructure; D009840:Oligomycins / Q000494:pharmacology; D009861:Onium Compounds / Q000378:metabolism; D017494:Proton Pumps / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011522:Protons; D012413:Rubidium / Q000378:metabolism; D012457:Salicylamides / Q000494:pharmacology; D014320:Triphenylmethyl Compounds / Q000378:metabolism; D014344:Trypanocidal Agents / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*
D009840:Oligomycins; D009861:Onium Compounds; D017494:Proton Pumps; D011522:Protons; D012457:Salicylamides; D014320:Triphenylmethyl Compounds; D014344:Trypanocidal Agents; C011561:triphenylmethylphosphonium; C005703:salicylhydroxamic acid; D006180:Proton-Translocating ATPases; D012413:Rubidium