Kinetics of Phosphorylation of eIF-2 by the hemin-controlled repressor and casein kinase II. Inhibition by hemin and 2,3-diphosphoglyceric acid.
The kinetics of phosphorylation of eukaryotic initiation factor 2 (eIF-2) by two cyclic nucleotide-independent protein kinases from rabbit reticulocytes have been studied. The hemin-controlled repressor (HCR) and casein kinase II phosphorylate the alpha and beta subunits of eIF-2, respectively. The apparent Km for eIF-2 with HCR and casein kinase II was determined to be in the range of 0.5-1.0 microM. Using fully dephosphorylated eIF-2, it was possible to show that the phosphorylation state of the beta subunit did not affect the apparent Km of either HCR or casein kinase II for eIF-2. The effects of two inhibitory compounds, hemin and 2,3-diphosphoglyceric acid (2,3-DPG), were studied also. Hemin acted as a noncompetitive inhibitor of HCR with respect to eIF-2 with an apparent Ki of 3 microM, while inhibition of casein kinase II by 2,3-DPG was competitive with respect to eIF-2. The apparent inhibitory constant was determined to be 1 mM, a concentration within the physiological range of 2,3-DPG in red blood cells. From the kinetic values obtained with hemin and 2,3-DPG, it appears that these compounds could directly regulate the respective protein kinases in vivo.
D019794:2,3-Diphosphoglycerate; D000818:Animals; D047388:Casein Kinases; D004163:Diphosphoglyceric Acids / Q000494:pharmacology*; D015852:Eukaryotic Initiation Factor-2; D006418:Heme / Q000031:analogs & derivatives*; D006427:Hemin / Q000494:pharmacology*; D006736:Horses; D007700:Kinetics; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects*; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism* / Q000494:pharmacology*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology; D019892:eIF-2 Kinase
D004163:Diphosphoglyceric Acids; D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors; D011506:Proteins; D019794:2,3-Diphosphoglycerate; D006418:Heme; D006427:Hemin; D011494:Protein Kinases; D047388:Casein Kinases; D019892:eIF-2 Kinase