Transport of proteins into mitochondria

Translocational intermediates of precursor proteins of ATPase F1β
subunit and cytochrome c1 across mitochondrial membranes were
analyzed using two different approaches, transport at low
temperature and transport after binding of precursor proteins to
antibodies. Under both conditions precursors were partially
transported into mitochondria in an energy-dependent manner. They
were processed by the metalloprotease in the matrix but a major
proportion of the polypeptide chains was still present at the outer
face of the outer mitochondrial membrane. We conclude that transfer
of precursors into the inner membrane or matrix space occurs
through “translocation contact sites”; precursor polypeptides to
F1β and cytochrome c1 enter the matrix space with the amino
terminus first; and a membrane potential is required for the
transmembrane movement on an amino-terminal “domain-like” structure
but not for completing translocation of the major part of the
polypeptides.