Transport of proteins into mitochondria: a potassium diffusion potential is able to drive the import of ADP/ATP carrier

The mitochondrial ADP/ATP carrier is an integral transmembrane protein of the inner mem-brane. It is synthesized on cytoplasmic ribosomes. Kinetic data suggested that this protein is trans-ferred into mitochondria in a posttranslational manner. The following results provide further evidence for such a mechanism and provide information on its details. 1. In homologous and heterologous translation systems the newly synthesized ADPjATP carrier protein is present in the postribosomal supernatant. 2. Analysis by density gradient centrifugation and gel filtration shows, that the ADPjATP carrier molecules in the postribosomal fraction are present as soluble complexes with apparent molecular weights of about I20000 and 500000 or larger. The carrier binds detergents such as Triton X-I 00 and deoxycholate forming mixed micelles with molecular weights of about 200000-400 000. 3. Incubation of a postribosomal supernatant of a reticulocyte lysate containing newly syn-thesized ADP/ATP carrier with mitochondria isolated from N~zrrosporu spheroplasts results in efficient transfer of the carrier into mitochondria. About 20-30", of the transferred carrier are resistant to proteinase in whole mitochondria. The authentic mature protein is also largely resistan