Transport of proteins into mitochondria

The transfer of cytoplasmically synthesized precursor proteins into
or across the inner mitochondrial membrane is dependent on
energization of the membrane. To investigate the role of this
energy requirement, a buffer system was developed in which
efficient import of ADP/ATP carrier into mitochondria from the
receptor-bound state occurred. This import was rapid and was
dependent on divalent cations, whereas the binding of precursor
proteins to the mitochondrial surface was slow and was independent
of added divalent cations. Using this buffer system, the import of
ADP/ATP carrier could be driven by a valinomycin-induced potassium
diffusion potential. The protonophore carbonylcyanide
m-chlorophenyl-hydrazone was not able to abolish this import.
Imposition of a delta pH did not stimulate the import. We conclude
that the membrane potential delta psi itself and not the total
protonmotive force delta p is the required energy source.