Kinetic and Mechanistic Analysis of Dinucleotide and Oligonucleotide Formation from the 5'-Phosphorimidazolide of Adenosine on Na+-Montmorillonite

Abstract

The rate constants for the condensation reaction of the 5'-phosphorimidazolide of adenosine (ImpA) to form dinucleotides and oligonucleotides have been measured in the presence of Na(+)-volclay (a Na(+)-montmorillonite) in pH 8 aqueous solution at 25 degrees C. The rates of the reaction of ImpA with an excess of adenosine 5'-monophosphoramidate (NH2pA), P1,P2-diadenosine 5',5'-pyrophosphate (A5'ppA), or adenosine 5'-monophosphate (5'-AMP or pA) in the presence of the montmorillonite to form NH2pA3'pA, A5'ppA3'pA, and pA3'pA, respectively, were measured. Only 3',5'-linked products were observed. The magnitude of the rate constants decrease in the order NH2pA3'pA > A5'-ppA3'pA > pA3'pA. The binding of ImpA to montmorillonite was measured, and the adsorption isotherm was determined. The binding of ImpA to montmorillonite and the formation of higher oligonucleotides is not observed in the absence of salts. Mg2+ enhances binding and oligonucleotide formation more than Ca2+ and Na+. The rate constants for the oligonucleotide formation were determined from the reaction products formed from 10 to 40 mM ImpA in the presence of Na(+)-montmorillonite using the computer program SIMFIT. The magnitudes of the rate constants for the formation of oligonucleotides increased in the order 2-mer < 3-mer < 4-mer ... 7-mer. The rate constants for dinucleotide and trinucleotide formation are more than 1000 times larger than those measured in the absence of montmorillonite. The rate constants for the formation of dinucleotide, trinucleotide, and tetranucleotide are 41,2.6, and 3.7 times larger than those for the formation of oligo(G)s with a poly(C) template. The hydrolysis of ImpA was accelerated 35 times in the presence of the montmorillonite. The catalytic ability of montmorillonite to form dinucleotides and oligonucleotides is quantitatively evaluated and possible pathways for oligo(A) formation are proposed.

Self-organizing biochemical cycles

“…However, the very limited studies in prebiotic chemistry relevant to this hypothesis have not uncovered any highly regiospecific reactions. Ferris and his coworkers (25,26) have shown that montmorillonite catalyzes the oligomerization of adenosine 5Ј-phosphorimidazolide and leads to the formation of oligomers substantially enriched in 3Ј-5Ј phosphodiester bonds. However, the regiospecificity is only about 80%, less than the regiospecificity in favor of 2Ј-5Ј-bonds of the uncatalyzed reaction.…”

Os semimetais na origem e evolução da vida

“…O mecanismo de catálise da polimerização de nucleótidos por argilas montemorilonite não é totalmente conhecido, mas o desempenho do silício pode não ser relevante. 72,[74][75][76][77] …”

Montmorillonite-catalysed formation of RNA oligomers: the possible role of catalysis in the origins of life

“…As noted above, the rate constant for the montmorillonite-catalysed oligomerization of 5 0 -phosphorimidazolide of adenosine is 100-1000 times greater than the rate of its hydrolysis. Hydrolysis is the main reaction product in the absence of montmorillonite along with a few percentage of dimers, where the rate constant of oligomer formation is only 10 times that of hydrolysis (Kawamura & Ferris 1994;Kanavarioti 1997).…”