Purification and properties of eIF-2 phosphatase.
Eukaryotic initiation factor 2 (eIF-2) phosphatase has been purified 840-fold to apparent homogeneity from rabbit reticulocyte lysate. Native eIF-2 phosphatase has a Mr = 98,000, pI = 6.1, s20,w = 5.1, and a Stokes radius = 38 A. A subunit composition of one 60,000-dalton polypeptide and one 38,000-dalton polypeptide is indicated. The Km for [32P]eIF-2 is 30 microM and the Vmax = 1.1 nmol of phosphate released/min/microgram. The 38,000-dalton subunit of eIF-2 phosphatase does not co-electrophorese with the catalytic subunit of liver phosphorylase phosphatase, a type 1 protein phosphatase. The specificity of eIF-2 phosphatase for phosphorylation sites on th alpha- and beta-subunits of eIF-2 appears to be determined by the environment of the phosphatase and substrate. Both the alpha- and beta-subunits of [32P]eIF-2 are rapidly dephosphorylated by the purified phosphatase. In unfractionated lysate and in unfractionated lysate supplemented with an equivalent activity of the purified phosphatase, only the alpha-subunit of eIF-2 is dephosphorylated. This indicates other factors are present in the lysate which govern the dephosphorylation of eIF-2.
D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007526:Isoelectric Point; D007700:Kinetics; D008970:Molecular Weight; D010448:Peptide Initiation Factors / Q000097:blood / Q000302:isolation & purification; D010749:Phosphoprotein Phosphatases / Q000097:blood / Q000302:isolation & purification*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*; D013379:Substrate Specificity
D010448:Peptide Initiation Factors; C019363:eIF-2 phosphatase; D010749:Phosphoprotein Phosphatases