flavin-adenine-dinucleotide and Hepatoblastoma

Rat dimethylglycine dehydrogenase (Me2GlyDH) was used as model protein to study the biogenesis of a covalently flavinylated mitochondrial enzyme. Here we show that: 1) enzymatically active holoenzyme correlated with trypsin resistance of the protein; 2) folding of the reticulocyte lysate-translated protein into the trypsin-resistant, holoenzyme form was a slow process that was stimulated by the presence of the flavin cofactor and was more efficient at 15 degrees C than at 30 degrees C; 3) the mitochondrial presequence reduced the extent but did not prevent holoenzyme formation; 4) covalent attachment of FAD to the Me2GlyDH apoenzyme proceeded spontaneously and did not require a mitochondrial protein factor; 5) in vitro only the precursor, but not the mature form, of the protein was imported into isolated rat liver mitochondria; in vivo, in stably transfected HepG2 cells, both the precursor and the mature form were imported into the organelle; 6) holoenzyme formation in the cytoplasm did not prevent the translocation of the proteins into the mitochondria in vivo; and 7) lack of vitamin B2 in the tissue culture medium resulted in a reduced recovery of the precursor and the mature form of Me2GlyDH from cell mitochondria, suggesting a decreased efficiency of mitochondrial protein import.

Topics: Amino Acid Sequence; Animals; Base Sequence; Cell Line; Cloning, Molecular; Dimethylglycine Dehydrogenase; Flavin-Adenine Dinucleotide; Gene Expression; Hepatoblastoma; Humans; Kinetics; Liver Neoplasms; Methionine; Mitochondria, Liver; Mitochondrial Proteins; Molecular Sequence Data; Oligodeoxyribonucleotides; Oxidoreductases, N-Demethylating; Protein Biosynthesis; Protein Processing, Post-Translational; Rats; Recombinant Proteins; Sulfur Radioisotopes; Transfection; Tumor Cells, Cultured