Presence of haemin-controlled eIF-2 alpha kinases in both undifferentiated and differentiating mouse erythroleukaemia cells.
In rabbit reticulocytes, globin synthesis is regulated by a haemin-controlled translational inhibitor (HCI) which acts by phosphorylating the alpha-subunit of eukaryotic initiation factor 2 (eIF-2). With purified eIF-2 as substrate, haemin-controlled eIF-2 alpha kinases could be partially purified from cultured mouse erythroleukaemia cells (MEL cells), which can be induced in vivo to erythroid differentiation. The eIF-2 alpha kinases from both uninduced and induced MEL cells are clearly distinct from the double-stranded-RNA-activated eIF-2 alpha kinase described for many mammalian cell types. A rough quantitative estimation indicates that, on a per-cell basis, induced MEL cells contain the same amount of haemin-controlled eIF-2 alpha kinase activity as rabbit reticulocytes, whereas uninduced MEL cells contain about one-tenth as much. As to their chromatographic behavior on CM-Sephadex and DEAE-cellulose and their sensitivity towards physiological concentrations of haemin (5-10 microM), the eIF-2 alpha kinases from MEL cells are indistinguishable from HCI. They differ from HCI with respect to their response towards activating stimuli such as prolonged incubation at 37 degrees C or brief exposure to the thiol reagent N-ethylmaleimide.
Sarre
T F
TF
Institut für Biologie III, Albert-Ludwigs-Universität Freiburg, Federal Republic of Germany.
D000818:Animals; D002454:Cell Differentiation; D004912:Erythrocytes / Q000166:cytology; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology* / Q000473:pathology; D051379:Mice; D011494:Protein Kinases / Q000097:blood*; D014407:Tumor Cells, Cultured / Q000201:enzymology / Q000473:pathology; D019892:eIF-2 Kinase
D011494:Protein Kinases; D019892:eIF-2 Kinase