Biogenesis of the mitochondrial matrix enzyme, glutamate dehydrogenase, in rat liver cells. I. Subcellular localization, biosynthesis, and intracellular translocation of glutamate dehydrogenase.

1. The presence of glutamate dehydrogenase in the microsomal fraction of rat liver was confirmed. The identities of mitochondrial and microsomal glutamate dehydrogenases were proved by immunochemical methods and by SDS polyacrylamide gel electrophoresis of purified enzymes. 2. Synthesis of glutamate dehydrogenase by the membrane-bound ribosomes of rough endoplasmic reticulum was determined. Newly synthesized enzyme molecules were discharged on the cytoplasmic surface of endoplasmic reticulum membranes. 3. A precursor-product relationship was found between microsomal and mitochondrial glutamate dehydrogenases. About six hours were needed for the transport of glutamate dehydrogenase from the site of synthesis to mitochondria. 4. The half-life of glutamate dehydrogenase was about 5.5 days, which was somewhat longer than that of mitochondrial total protein determined in the same experiment. 5. Mitochondrial-type malate dehydrogenase was also present in the microsomal fraction. Subfractionation of smooth microsomes revealed the existence of particular light microsomal vesicles in which both glutamate dehydrogenase and malate dehydrogenase were concentrated. These vesicles may participate in intracellular transport of matrix enzymes from microsomes to mitochondria.