title: Magnesium ion catalyzed P-N bond hydrolysis in imidazolide-activated nucleotides.  Relevance to template-directed synthesis of polynucleotides.
abstract: Magnesium, an ion necessary in enzymatic as well as in nonenzymatic template-directed polynucleotide-synthesizing reactions, has been found to catalyze the hydroxide ion attack on the P-N bond of selected 5'-monophosphate imidazolide derivatives of nucleotides, such as guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG), guanosine 5'-monophosphate imidazolide (ImpG), and adenosine 5-monophosphate 2-methylimidazolide (2-MeImpA).  Calcium ion behaves similarly, but quantitatively the effects are smaller.  Pseudo-first-order rate constants of 2-MeImpG and ImpG hydrolysis as a function of Mg2+ concentration have been obtained in the range 6 < or = pH < or = 10 at 37 degrees C.  Mg2+ catalysis is particularly effective around pH 10 where a 0.02 M concentration leads to 15-fold acceleration and a 0.2 M concentration to a 115-fold acceleration of the rate.  At other pH values Mg2+ catalysis is less dramatic, mainly because the noncatalyzed reaction is faster.  Mg2+ catalysis is attributed to the reaction of the zwitterionic form of the substrate (SH+/-, imidazolide moiety protonated) with OH- rather than reaction of the anionic form (S-, imidazolide moiety deprotonated) with water.  This conclusion is based on a study of the N-methylated substrates N-MeImpG and 1,2-diMeImpg, respectively, which were generated in situ by the equilibrium reaction of ImpG with N-methylimidazole and 2-MeImpG with 1,2-dimethylimidazole, respectively.  In contrast, the absence of Mg2+ the reaction of S- with water competes with the reaction of SH+/- with OH-.  The present study bears on the mechanism of the Mg2(+)-catalyzed template-directed synthesis of oligo-and polynucleotides derived from 2-MeImpG and on the competition between oligonucleotide synthesis and hydrolysis of 2-MeImpG.
authors.affiliation: Chemistry Department, University of California, Santa Cruz 95064, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kanavarioti
authors.forename: C F
authors.initials: CF
authors.lastname: Bernasconi
authors.forename: D L
authors.initials: DL
authors.lastname: Doodokyan
authors.forename: D J
authors.initials: DJ
authors.lastname: Alberas
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002384:Catalysis; D019143:Evolution, Molecular; D006157:Guanosine Monophosphate / Q000031:analogs & derivatives / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D009711:Nucleotides / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D011119:Polynucleotides / Q000138:chemical synthesis*; D013698:Templates, Genetic
chemical_list: D009711:Nucleotides; D011119:Polynucleotides; D010758:Phosphorus; C025339:guanosine 5'-phosphoimidazolide; C036896:guanosine 5'-phospho-2-methylimidazolide; D006157:Guanosine Monophosphate; D008274:Magnesium; D009584:Nitrogen; D002118:Calcium