The deamination of cytosine: an ab initio SCF mo study

Abstract

In 1974, Lindahl and Nyberg studied the rate of deamination of cytokine residues in single and double stranded DNA. After studying the rate at several temperatures the activation energy for the conversion of cytosine to uracil was estimated to be 121 kJ/mol. -- Possible mechanisms for deamination of cytosine are studied using ab initio SCF molecular orbital calculations. Ab initio calculations with STO-3G, 3-21G and 6-31G* basis sets have been performed to investigate the optimized structures and energies. -- First the deamination of amidine is studied as a model compound and the calculations are then extended to cytosine. The results for both calculations indicate that the rate-determining step (second step) with OH- has a barrier of 209 kJ/mol and with H₂O has a barrier of 174 kJ/mol. The results show that the reaction is hermodynamically favourable but kinetically not very favourable.