Transport of F1-ATPase subunit beta 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 delta psi by the action of the F0F1-ATPase. Under these conditions, import of subunit beta of F1-ATPase (F1 beta) was inhibited. Addition of ATP or GTP restored import. When the membrane potential was destroyed, however, the import of F1 beta was completely inhibited even in the presence of ATP. We therefore conclude that the import of F1 beta depends on both nucleoside triphosphates and a membrane potential.