title: Detection of a proton-transfer process by kinetic solvent isotope effects in NH(4)(+)-mediated reactions catalyzed by a hammerhead ribozyme.
abstract: Hammerhead ribozymes have been considered to be metalloenzymes. However, this proposal was recently questioned by the finding that the reaction proceeds in the presence of high concentrations of monovalent ions such as NH(4)(+) ions and in the absence of any divalent metal ions. Our present analysis based on solvent isotope effects indicates that (1) a proton transfer(s) occurs only in the NH(4)(+)-mediated reaction but not in metal-ion-mediated reactions such as Mg(2+)- and Li(+)-mediated reactions, (2) the catalyst that stabilizes the 5' leaving group in the NH(4)(+)-mediated reaction is different from that in the metal-ion-mediated HH ribozyme reactions, (3) an NH(4)(+) ion seems to act as a general acid catalyst, and (4) a nucleobase alone should not be the catalyst.
authors.affiliation: Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, Hongo, Tokyo 113-8656, Japan.
authors.forename: Yasuomi
authors.initials: Y
authors.lastname: Takagi
authors.forename: Kazunari
authors.initials: K
authors.lastname: Taira
mesh_terms: D001483:Base Sequence; D002384:Catalysis; D002412:Cations; D003903:Deuterium; D007700:Kinetics; D008094:Lithium / Q000737:chemistry / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D009690:Nucleic Acid Conformation; D011522:Protons; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D016337:RNA, Catalytic / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002412:Cations; D011522:Protons; D000644:Quaternary Ammonium Compounds; D016337:RNA, Catalytic; C427204:hammerhead ribozyme; D008094:Lithium; D003903:Deuterium; D008274:Magnesium