Protein synthesis by brain-cortes mitochondria. Characterization of a 55S mitochondrial ribosome as the functional unit in protein synthesis by cortex mitochondria and its distinction from a contaminant cytoplasmic protein-synthesizing system.
Homogenates of rat brain cortex were fractionated by conventional methods of velocity sedimentation and separated into a microsomal and a washed mitochondrial fraction. By electron microscopy the mitochondrial fraction was shown to be rich in synaptosomes. The mitochondria-synaptosome fraction synthesized protein in vitro by a route that was partially inhibited by cycloheximide and partly by chloramphenicol. The relative effectiveness of the two inhibitors varied greatly with the medium used. In the mitochondria-synaptosome fraction active 80S cytoplasmic ribosomes and active 55S mitochondrial ribosomes were detected; these were also seen in the electron microscope. Mild osmotic shock of the mitochondria-synaptosome fraction followed by velocity sedimentation in sucrose-EDTA allowed isolation of a mitochondrial fraction free of synaptosomes. Protein synthesis in this fraction was entirely inhibited by chloramphenicol, but was completely resistant to cycloheximide both in a medium promoting oxidative phosphorylation and in ATP-generating medium. Ouabain had no inhibitory effect on protein synthesis in a purified mitochondrial preparation. It is concluded that brain-cortex mitochondria synthesize protein entirely on 55S mitochondrial ribosomes.
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002499:Centrifugation, Density Gradient; D002540:Cerebral Cortex / Q000378:metabolism*; D002701:Chloramphenicol / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010085:Oxidative Phosphorylation; D014176:Protein Biosynthesis; D011691:Puromycin / Q000494:pharmacology; D051381:Rats; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism
D000596:Amino Acids; D011691:Puromycin; D010042:Ouabain; D002701:Chloramphenicol; D000255:Adenosine Triphosphate; D003513:Cycloheximide