Regulation of malic enzyme synthesis by thyroid hormone and glucagon: inhibitor and kinetic experiments.
Synthesis of malic enzyme was rapidly and markedly stimulated by the addition of triiodothyronine to chick embryo liver cells in culture. Alpha-Amanitin, an inhibitor of DNA-dependent RNA polymerase II, blocked induction. The kinetics of induction and de-induction of malic enzyme synthesis suggested that the most stable event in triiodothyronine induction had a half-life of 18 to 20 h. However, malic enzyme synthesis decayed with a half-life of 2,4 h when transcription was inhibited with alpha-amanitin. Thus a long-lived event in thyroid hormone stimulation of malic enzyme synthesis occurred prior to transcription of a specific messenger RNA (mRNA), presumably malic enzyme mRNA. Malic enzyme synthesis decayed with a half-life of about 2 h when glucagon was added to pre-induced liver cells. The similarity of decay rates after inhibition of transcription with alpha-amanitin or inhibition of malic enzyme synthesis by glucagon suggests that glucagon may inhibit the transcription or processing of a specific mRNA required for malic enzyme synthesis.
D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D004790:Enzyme Induction / Q000187:drug effects; D005934:Glucagon / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000096:biosynthesis*; D014176:Protein Biosynthesis / Q000187:drug effects; D014284:Triiodothyronine / Q000494:pharmacology*
D000546:Amanitins; D014284:Triiodothyronine; D005934:Glucagon; D008291:Malate Dehydrogenase