title: Kinetic studies on the activation of eukaryotic peptidyltransferase by potassium.
abstract: In an effort to elucidate the role of potassium ions in the formation of peptide bond, we have used the reaction between puromycin and a ribosomal complex (from rabbit reticulocytes) bearing the donor substrate, AcPhe-tRNA, prebound at the so-called P site (puromycin-reactive state). This reaction can be analyzed as a first-order reaction. At saturating concentrations of puromycin (S) the first-order rate constant (k(max)S) is a measure of the apparent catalytic rate constant of peptidyltransferase in the puromycin reaction. This k(max)S depends on the concentration of potassium ions and increases when the concentration of K+ is increased. The data suggest a kinetic model in which potassium acts as an essential activator in the puromycin reaction. A single molecule of potassium participates in the mechanism of activation. The kinetics correspond to a sequential addition of potassium and puromycin to two separate and independent sites on the ribosome. At saturating levels of both K+ and S the maximal value for the catalytic rate constant of peptidyltransferase (k(p)) is equal to 20 min(-1) at 25 degrees C.
authors.affiliation: Department of Biochemistry, School of Medicine, University of Patras, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Ioannou
authors.forename: C
authors.initials: C
authors.lastname: Coutsogeorgopoulos
mesh_terms: D000818:Animals; D002414:Cations, Monovalent / Q000494:pharmacology; D002474:Cell-Free System; D004305:Dose-Response Relationship, Drug; D005057:Eukaryotic Cells / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D010452:Peptide Biosynthesis; D010458:Peptidyl Transferases / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects*; D011691:Puromycin / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism
chemical_list: D002414:Cations, Monovalent; D011691:Puromycin; D010458:Peptidyl Transferases; D011188:Potassium