title: Characterization of a rat liver factor that inhibits initiation of protein synthesis in rabbit reticulocyte lysates.
abstract: Protein synthesis in rabbit reticulocytes and their lysates is regulated by heme. In heme-deficient reticulocyte lysates, protein synthesis proceeds at the initial rate for several minutes and then declines abruptly. Inhibition of protein synthesis is due to the activation of a heme-regulated translational inhibitor (HRI) which blocks the initiation of protein synthesis. Addition of the isolated HRI to hemin-supplemented lysates causes inhibition of initiation similar to that observed in heme-deficiency. HRI has been shown to be a protein kinase that specifically phosphorylates the Met-tRNA(f) binding factor (eIF-2). We have isolated an inhibitor (LI) of protein chain initiation from rat liver which displays properties similar to those of HRI: (i) the chromatographic behavior of LI on DEAE-Sephadex, DEAE-cellulose, and phosphocellulose is similar to that of HRI; (ii) both LI and HRI inhibit protein chain initiation in rabbit reticulocyte lysates with the same kinetics of inhibition-i.e., an initial period of synthesis for several minutes at the control rate followed by an abrupt decline in the rate of initiation; (iii) both inhibitions are prevented or reversed by eIF-2; (iv) GTP (2 mM) prevents, and ATP (2 mM) potentiates, the inhibition of protein synthesis induced by either inhibitor; (v) LI is associated with a protein kinase that also phosphorylates the 38,000-dalton subunit of elF-2. These findings indicate that a mechanism for the regulation of protein synthesis similar to that found in rabbit reticulocytes may be present in rat liver.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000502:physiology*; D008297:Male; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D010448:Peptide Initiation Factors; D010477:Perfusion; D014176:Protein Biosynthesis / Q000187:drug effects*; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism; D011506:Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D010448:Peptide Initiation Factors; D011506:Proteins; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011494:Protein Kinases