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Limiting concentrations of activated mononucleotides necessary for poly(C)-directed elongation of oligoguanylatesSelected imidazolide-activated nucleotides have been subjected to hydrolysis under conditions similar to those that favor their template-directed oligomerization. Rate constants of hydrolysis of the P-N bond in guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG) and in guanosine 5'-monophosphate imidazolide (ImpG), kh, have been determined in the presence/absence of magnesium ion as a function of temperature and polycytidylate [poly(C)] concentration. Using the rate constant of hydrolysis of 2-MeImpG and the rate constant of elongation, i.e., the reaction of an oligoguanylate with 2-MeImpG in the presence of poly(C) acting as template, the limiting concentration of 2-MeImpG necessary for oligonucleotide elongation to compete with hydrolysis can be calculated. The limiting concentration is defined as the initial concentration of monomer that results in its equal consumption by hydrolysis and by elongation. These limiting concentrations of 2-MeImpG are found to be 1.7 mM at 37 degrees C and 0.36 mM at 1 degrees C. Boundary conditions in the form of limiting concentration of activated nucleotide may be used to evaluate a prebiotic model for chemical synthesis of biopolymers. For instance, the limiting concentration of monomer can be used as a basis of comparison among catalytic, but nonenzymatic, RNA-type systems. We also determined the rate constant of dimerization of 2-MeImpG, k2 = 0.45 +/- 0.06 M-1 h-1 in the absence of poly(C), and 0.45 +/- 0.06 less than or equal to k2 less than or equal to 0.97 +/- 0.13 M-1 h-1 in its presence at 37 degrees C and pH 7.95.(ABSTRACT TRUNCATED AT 250 WORDS).
Document ID
20050000865
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kanavarioti, A.
(University of California Santa Cruz 95064)
Chang, S.
Alberas, D. J.
Date Acquired
August 22, 2013
Publication Date
December 1, 1990
Publication Information
Publication: Journal of molecular evolution
Volume: 31
Issue: 6
ISSN: 0022-2844
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Number 52-20
NASA Center ARC
NASA Discipline Exobiology
Non-NASA Center
NASA Program Exobiology

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