title: Allosteric activation of rabbit reticulocyte guanine nucleotide exchange factor activity by sugar phosphates and inositol phosphates.
abstract: Sugar phosphates are required to maintain active rates of translation in gel-filtered rabbit reticulocyte lysates. They may stimulate polypeptide chain initiation by acting as NADPH generators or by a direct interaction with initiation factor(s). We now provide evidence for the allosteric activation of the purified guanine nucleotide exchange factor (eIF-2B) by sugar phosphates and inositol phosphates. In the presence of microM fructose 1,6-bisphosphate, the rate of eIF-2B-catalyzed GDP/GTP exchange is increased approximately 2-fold. The half-maximal concentration for stimulation of eIF-2B activity (SC50) is 57 microM. The binding of GTP to isolated eIF-2B is stimulated 1.5-fold, whereas GTP-binding to ALP-treated eIF-2B is not affected by sugar phosphates. Inositol 1,4-bisphosphate, like fructose 1,6-bisphosphate, stimulates 2-3-fold the activity of the isolated eIF-2B (SC50, 140 microM).
authors.affiliation: Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216, USA.
authors.forename: L P
authors.initials: LP
authors.lastname: Singh
authors.forename: A J
authors.initials: AJ
authors.lastname: Wahba
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D005635:Fructosediphosphates / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*
chemical_list: D005635:Fructosediphosphates; D020662:Guanine Nucleotide Exchange Factors; D007295:Inositol Phosphates; D011506:Proteins; D006153:Guanosine Diphosphate; C044259:inositol 1,4-bis(phosphate); D006160:Guanosine Triphosphate; C029063:fructose-1,6-diphosphate