Transport of F1-ATPase subunit β into mitochondria depends on both a membrane potential and nucleoside triphosphates

Transport of cytoplasmically synthesized precursor proteins into or
across the inner mitochondrial membrane requires a mitochondrial
membrane potential. We have studied whether additional energy
sources are also necessary for protein translocation. Reticulocyte
lysate (containing radiolabelled precursor proteins) and
mitochondria were depleted of ATP by pre-incubation with apyrase. A
membrane potential was then established by the addition of
substrates of the electron transport chain. Oligomycin was included
to prevent dissipation of Δψ by the action of the F0F1-ATPase.
Under these conditions, import of subunit β of F1-ATPase (F1β) was
inhibited. Addition of ATP or GTP restored import. When the
membrane potential was destroyed, however, the import of F1β was
completely inhibited even in the presence of ATP. We therefore
conclude that the import of F1β depends on both nucleoside
triphosphates and a membrane potential.