A possible correlation between the effects of some carcinogenic agents and the electronic structure of DNA.

The values of the quantum mechanical overlap integrals between the ~-orbitals of the superimposed nucleotide bases of DNA show that there is a non-negligible interaction between these bases. The energy levels of the MO's of the adenine-thymine and guanine-cytosine base pairs, known from the literature, differ from each other only by an amount -~0.09 8, which is the width of the second filled energy band of the protein molecule, whereas the overlap integral between the adjacent nucleotide bases is considerably larger than between the parallel polypeptide chains of protein. Therefore, it might be expected that in the DNA macromolecule the energies of the delocalized ~-electrons form energy bands. On the basis of the MO energies of the nucleotide base pairs one can show qualitatively that the energy bands of the DNA molecule are situated in such a manner that the hypotheses for the cancerous effect of radiation and of carcinogenic hydrocarbons, based on the quantum mechanical investigation of the electronic structure of protein, can also be applied to the electronic structure of the DNA molecule. I t is understandable that excitation or ionization of the molecule causes the polarization of the double helix forming the DNA, if the molecule within the cell is affected by an electric field parallel to its axis. We show in the paper that the repulsion energy between the two helices of DNA, caused by the appearance of an electric net charge of e0 at any end of the macromolecule, may induce with great probability the unwinding of the double helix. Further, we discuss two possibilities for the connection between the unwinding of the DNA particles and the beginning of tumor development. To support our hypothesis we continue, on the one hand, our quantum mechanical computations concerning the electronic structure of the DNA; on the other hand, preparations are under way for experimental investigations offcultures of cancerous tissues placed in strong electrostatic fields.