title: Analyses of kinetic solvent isotope effects of a hammerhead ribozyme reaction in NH4+ and Li+ ions.
abstract: Hammerhead ribozymes have been considered to be divalent-metalloenzymes. However, this was recently questioned by the finding that the reaction can proceed without any divalent metal ions in the presence of high concentrations of monovalent ions such as NH4+/Li+ ions. Thus, one might think divalent metal ions are not involved in chemical step in the catalytic mechanism. To investigate the involvement of the monovalent ions, we analyzed the deuterium solvent isotope effects in the reactions. Our present analysis indicates a proton transfer(s) occurs only in the NH(4+)-mediated reaction, not in the Li(+)-mediated. Most simple interpretation is that NH4+ works as a general acid catalyst and Li+ as Lewis acid catalyst. This suggests hammerhead ribozymes can change catalyst upon their surrounding conditions.
authors.affiliation: Genofunction Co. Ltd., Gene Discovery Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba Science City 305-8562, Japan.
authors.forename: Yasuomi
authors.initials: Y
authors.lastname: Takagi
authors.forename: Kazunari
authors.initials: K
authors.lastname: Taira
mesh_terms: D001483:Base Sequence; D002414:Cations, Monovalent; D007554:Isotopes; D007700:Kinetics; D008094:Lithium / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D016337:RNA, Catalytic / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002414:Cations, Monovalent; D007554:Isotopes; D000644:Quaternary Ammonium Compounds; D016337:RNA, Catalytic; D008094:Lithium