title: Phosphorylation and guanine nucleotide exchange on polypeptide chain initiation factor-2 from Artemia embryos.
abstract: Eukaryotic initiation factor-2 (eIF-2) from Artemia embryos is able to exchange guanine nucleotides at the same rate in the presence or absence of Mg2+ when the reaction is carried out with either purified eIF-2 at 30 degrees C or less purified preparations at any temperature (10-30 degrees C). No exchange factor appears to catalyze this reaction. However, with purified eIF-2 at lower temperatures (10 degrees C) the exchange is clearly impaired by Mg2+ and this impairment is overcome by the guanine nucleotide exchange factor (GEF) of rabbit reticulocytes. Thus, Artemia eIF-2 is able to exchange guanine nucleotides by two alternative mechanisms that may reflect two states of the protein. Phosphorylation of the eIF-2 alpha subunit by the heme-controlled inhibitor (HCI) of rabbit reticulocytes abolishes the GEF-dependent reaction, but has no effect on the factor-independent one. The search for eIF-2 alpha kinases in Artemia embryo led to the detection of only one such enzyme, which was identified as a casein kinase type II. None of the exchange reactions is affected by the phosphorylation of the eIF-2 alpha subunit by this kinase, suggesting that, irrespective of the kind of mechanism for guanine nucleotide exchange that is actually operating in Artemia, it might not be a target for regulation by eIF-2 alpha phosphorylation.
authors.affiliation: Centro de Biología Molecular, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: M G
authors.initials: MG
authors.lastname: Mateu
authors.forename: F G
authors.initials: FG
authors.lastname: Maroto
authors.forename: O
authors.initials: O
authors.lastname: Vicente
authors.forename: J M
authors.initials: JM
authors.lastname: Sierra
mesh_terms: D000818:Animals; D001156:Artemia / Q000196:embryology / Q000201:enzymology / Q000378:metabolism*; D047388:Casein Kinases; D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides / Q000378:metabolism*; D006851:Hydrochloric Acid / Q000494:pharmacology; D008274:Magnesium / Q000502:physiology; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism* / Q000502:physiology; D011817:Rabbits; D013696:Temperature; D019892:eIF-2 Kinase
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides; D010448:Peptide Initiation Factors; D011506:Proteins; D011494:Protein Kinases; D047388:Casein Kinases; D019892:eIF-2 Kinase; D008274:Magnesium; D006851:Hydrochloric Acid