Synthesis and intracellular transport of cytochrome oxidase subunit IV and ADP/ATP translocator protein in intact hepatoma cells (original) (raw)

The biosynthesis of two mitochondrial membrsne proteins-subunit IV of cytochroi~e oxidese and ADP/ATP translocator protein was studied in intact ascites hepetome cells. Using pulse-chase labeling and rapid cell fractionation it was possible to identify the precursoric forms of these inner mitochondrial membrane proteins. It was found that the subunit IV of cytochrome oxidase is synthesized in the cytoplasm of mammalian cells in the form of s larger precursor while ADP/ATP translocator protein is synthesized in the form that is electrophoretically undistinguishable from the msture membrane integrated form. The major part of mitochondrial proteins is synthesized on the cytoplasmic ribosomes end consequently transported to the mitochondris /i/. With few exceptions these impozted proteins are initially synthesized in the form of larger precursors /2,3/. The characterization of these precursors and the events involved in their posttrsnslationsl fate have been extensively studied in yesst and fungi /2-7/. Most of the corresponding studies with msmmalisn cells ~ere performed using heterologous cell-free protein synthesizing systems /8-11/. Physiologically more relevant systems hsve been employed only in s limited extent. Consequently, the information on the intrscelluler synthesis, transport and processing of mitochondriel proteins in intact mammalian cells are restrained to two soluble mitochondrial