Hydrogen-deuterium exchange in nucleosides and nucleotides. A mechanism for exchange of the exocyclic amino hydrogens of adenosine.
Biochemistry, 1975/6/17;14(12):2745-9.
PMID: 238573
Impact factor: 3.321
Abstract
The pH dependence of the apparent first-order rate constant for the exchange of the exocyclic amino hydrogens of adenosine with deuterium from the solvent was measured by stopped-flow ultraviolet spectroscopy. This dependence shows acid catalysis, base catalysis, and spontaneous exchange at neutral pH values. A study of the effect of several buffers on the rates of exchange reveals both general acid and general base catalytic behavior for the exchange process. We propose a general mechanism for the exchange which requires N-1 protonated adenosine as an intermediate for the acid-catalyzed exchange and amidine anion for the base-catalyzed exchange. In both cases the rate-limiting step is the base-catalyzed abstraction of a proton from the exocyclic amino moiety. Evaluation of the rate constants predicts the equilibrium for the exocyclic amino/imino tautomers to be 6.3 times 10(3):1.
MeSH terms
Adenosine; Adenosine Monophosphate; Amines; Binding Sites; Deuterium; Dipeptides; Glycine; Hydrogen; Hydrogen-Ion Concentration; Imidazoles; Imines; Kinetics; Mathematics; Molecular Conformation; Spectrophotometry, Ultraviolet; Temperature; Thermodynamics; Time Factors
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