Purification of the putative import-receptor for the precursor of the mitochondrial protein.

The receptor protein for the mitochondrial protein precursor synthesized in the cytosol was extensively purified from the mitochondrial membrane fraction by affinity column chromatography using a synthetic peptide containing the extrapeptide of ornithine aminotransferase as a ligand. The purified fraction contained two major proteins with molecular masses of 52 and 29 kDa. Of these proteins, only the 29 kDa protein bound to the extrapeptide of ornithine aminotransferase. Furthermore, anti-29 kDa protein Fab fragments inhibited the import of pre-ornithine aminotransferase into mitochondria, suggesting that the 29 kDa protein plays an essential role in the process of import of the mitochondrial protein precursor.