Cytosolic and mitochondrial surface factor-independent import of a synthetic peptide into mitochondria

We chemically synthesized a peptide, 11β-45, which was composed of 45 amino acid residues including the whole extension peptide and some of the mature portion of bovine cytochrome P-450(11β) precursor. 11β-45 was imported into mitochondria in vitro depending on the mitochondrial membrane potential, but its import did not require extramitochondrial ATP. Although cytosolic protein factors in the high speed supernatant of reticulocyte lysate are known to stimulate the import of various precursor proteins into mitochondria, the import of 11β-45 was not stimulated by cytosolic factors in reticulocyte lysate. The import of the peptide did not require mitochondrial surface protein components because its import was not affected by trypsin treatment of mitochondria. On the other hand, trypsin treatment of mitoplasts resulted in a great reduction in the import of the peptide, indicating that 11β-45 interacts during the import process with some protein components located inside mitochondria. These observations indicated that the peptide 11β-45 was imported via the potential-dependent pathway as in the case of precursor proteins, but skipped the interactions with cytosolic factors and mitochondrial surface components normally required for the import of precursor proteins.