Biopolymers and cell. 1999; 15 (6): 487 - 492

Theoretical study of pyrimidine photohydrates and mechanism of mutagenic action of UV-light

V. I. Danilov, J. L. Alderfer

The quantum mechanical study for the ground state of normal and rare tautomeric forms of pyrimidine bases and their photohydrates has been performed by means of multi-configurational SCF method in frame of semiempirical Ham'dtonian AMI with full geometry optimization. Unlike the cytosine, it is detected that both rare hnino form conformations (trans and cys) of cytosine photohydrate are more stable than its normal amino form. Hydrution simulation of these compounds l>y the Monte Carlo method showed t/iai in the case of cytosine the water stabilizes more its amino form while in the case of cytosine photohydrate more stable becomes its imino form. The cytosine. photohydrate possesses an uracil similar struc¬ture, so it is able to form a base pair with adenine. As a result of G-C -» A-T(U) or C -» T(U) transitions occur during the nucleic-acids replicaton error. The data obtained serve an evidence that the tautomerism is a possible mechanism of UV-light mutagenic effect.