Ab Initio Study of the Prototropic Tautomerism of Cytosine and Guanine and Their Contribution to Spontaneous Point Mutations

doi:10.3390/i4070410

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Int. J. Mol. Sci. 2003, 4(7), 410-421; doi:10.3390/i4070410

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Ab Initio Study of the Prototropic Tautomerism of Cytosine and Guanine and Their Contribution to Spontaneous Point Mutations

Yevgeniy Podolyan, Leonid Gorb and Jerzy Leszczynski *

Computational Center for Molecular Structure and Interactions, Jackson State University, Department of Chemistry, 1325 J.R. Lynch St., Jackson, MS 39217-0510, USA

* Author to whom correspondence should be addressed.

Received: 7 April 2003; in revised form: / Accepted: 9 April 2003 / Published: 25 June 2003

(This article belongs to the Special Issue Proton Transfer Processes)

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Abstract: High-level quantum-chemical and quantum-dynamics calculations are reported on the tautomerization equilibria and rate constants of isolated and monohydrated cytosine and guanine molecules. The results are used to estimate the fraction of the bases present in the cell during DNA synthesis as the unwanted tautomers that forms irregular base pairs, thus giving rise to a spontaneous GC → AT point mutation. A comparison of the estimated mutation frequencies with the observed frequency in E. coli is used to analyze two proposed mechanisms, differing in the degree of equilibration reached in the tautomerization reaction. It was found that the fraction of the rare tautomer in monohydrated complex of cytosine as well as guanine significantly exceed the amount responsible for the observed values of the GC → AT mutations. In the absence of water the equilibrium concentration of tautomeric forms is relatively large, but the barrier to their formation is high. It is possible that the mechanism in which a high tautomerization barrier keeps the tautomeric transformation far from a state of equilibrium is more likely than a mechanism in which water and/or polymerases produce a low equilibrium concentration of the tautomeric forms.

Keywords: ab initio; quantum dynamics; spontaneous point mutations; tautomers; rate constants; equilibrium constants

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MDPI and ACS Style

Podolyan, Y.; Gorb, L.; Leszczynski, J. Ab Initio Study of the Prototropic Tautomerism of Cytosine and Guanine and Their Contribution to Spontaneous Point Mutations. Int. J. Mol. Sci. 2003, 4, 410-421.

AMA Style

Podolyan Y, Gorb L, Leszczynski J. Ab Initio Study of the Prototropic Tautomerism of Cytosine and Guanine and Their Contribution to Spontaneous Point Mutations. International Journal of Molecular Sciences. 2003; 4(7):410-421.

Chicago/Turabian Style

Podolyan, Yevgeniy; Gorb, Leonid; Leszczynski, Jerzy. 2003. "Ab Initio Study of the Prototropic Tautomerism of Cytosine and Guanine and Their Contribution to Spontaneous Point Mutations." Int. J. Mol. Sci. 4, no. 7: 410-421.

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