Mitochondrial protein import

Proteolytic degradation of receptor sites on the mitochondrial
surface strongly reduces the efficiency of mitochondrial protein
import. The remaining residual import still involves basic
mechanisms of protein import, including: insertion of precursors
into the outer membrane, requirement for ATP and a membrane
potential, and translocation through contact sites between both
membranes. The import of a chloroplast protein into isolated
mitochondria which occurs with a low rate is not inhibited by a
protease-pretreatment of mitochondria, indicating that this
precursor only follows the bypass pathway. The low efficiency of
bypass import suggests that this unspecific import does not disturb
the uniqueness of mitochondrial protein composition. We conclude
that mitochondrial protein import involves a series of steps in
which receptor sites appear to be responsible for the specificity
of protein uptake.