Polyamines Stimulate the “In Vitro” Transport of the Precursor of Ornithine Carbamoyltransferase into Rat Liver Mitochondria
Most mitochondrial proteins are coded by nuclear genes, synthesized outside mitochondria, and imported into these organelles in a post-translational event (1). The import process usually involves the following steps: 1) synthesis of a precursor polypeptides with an amino-terminal extension (signal peptide), on free cytoplasmic polysomes, 2) binding of the precursor to a receptor-like component on the mitochondrial surface, 3) energy-dependent translocation across both mitochondrial membranes, possibly through “contact sites” between outer and inner membranes, 4) removal of the amino-terminal extension by a chelator-sensitive protease in the mitochondrial matrix, and 5) mature proteins location into their functional sites. Exceptions to this sequence of events include apocytochrome c and all proteins of the outer membrane which are synthesized without a leading peptide and transported into mitochondria without need of a membrane potential.
KeywordsMitochondrial Protein Creatine Phosphate Contact Site Transport Medium Cytosolic Extract
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