Mechanism of hormonal induction of tyrosine aminotransferase studied by measurement of the concentration of growing enzyme molecules.
Proteins labeled in cultured hepatoma cells grown in the presence of radioactive amino acids and pactamycin consist primarily of growing polypeptide chains initiated before addition of the antibiotic. Nascent tyrosine aminotransferase (EC 2.6.1.5) molecules were labeled in this way, and their radioactivity after completion was measured immunologically. Cells exposed to the synthetic adrenal steroid, dexamethasone, contain 10- to 18- times as much nascent enzyme as uninduced cells. These results indicate that induction control is not at the level of polypeptide-chain elongation or release, but probably operates on either the amount of messenger RNA or the rate of specific polypeptide-chain initiation.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D000918:Antibody Specificity; D002247:Carbon Isotopes; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000378:metabolism; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D003907:Dexamethasone / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004790:Enzyme Induction / Q000187:drug effects; D007106:Immune Sera; D008113:Liver Neoplasms; D009363:Neoplasm Proteins / Q000096:biosynthesis; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D051381:Rats; D012756:Sheep / Q000276:immunology; D014316:Tritium; D014444:Tyrosine Transaminase / Q000096:biosynthesis*
D000596:Amino Acids; D000903:Antibiotics, Antineoplastic; D002247:Carbon Isotopes; D007106:Immune Sera; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D014316:Tritium; D003907:Dexamethasone; D014444:Tyrosine Transaminase