Control of eIF-2 phosphatase activity in rabbit reticulocyte lysate.
A sensitive assay requiring picomole amounts of [32P]eIF-2 to measure eIF-2 phosphatase activity has been developed. Dephosphorylation of [32P]eIF-2 alpha (38,000-dalton subunit) is extremely rapid (t 1/2 = 20 sec) and occurs at the same rate in both hemin-supplemented and hemin-depleted lysates. In contrast, [32P]eIF-2 beta phosphate is stable under all conditions studied. At concentrations required to produce a transient inhibition of protein synthesis, GDP prevents dephosphorylation of half of the phosphate introduced on eIF-2 alpha by the hemin-controlled repressor. Equimolar GTP is without effect. The concept that the energy charge of the guanylate pool may regulate accessibility of a phosphorylated site on eIF-2 alpha to its phosphatase and the implication of this to the mechanism of hemin-regulated translational control are discussed.
D000818:Animals; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D010442:Peptide Chain Initiation, Translational; D010749:Phosphoprotein Phosphatases / Q000097:blood*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*
D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C019363:eIF-2 phosphatase; D010749:Phosphoprotein Phosphatases