Degradation of Dry Deoxyribonucleic Acid by Polonium Alpha-Particles

Thin films of desoxyribonucleic acid were irradiated with alpha particles from polonium, and their physical properties were determined by light- scattering and viscosity measurements. The change in viscosity was the same for films containing 0, 20, and 80 parts of water per 100 parts of DNA; in this respect, alpha -irradiation is quite different from irradiation with 2-Mev electrons. So long as oxygen was present the molecular weight and the square of radius of gyration of the molecule fell in unison. All the data are consistent with the assumption that the molecule was severed. A main-chain break was produced for every 650 ev of energy deposited; this indicates that this process occurred whenever one alpha particle traversed a molecule of DNA. In the absence of oxygen the molecular weight did not fall; this was attributed to a limited amount of crosslinking which gave a branched molecule. The viscosity, unlike the molecular weight, was not affected by branching. The crosslinking was ascribed, by analogy with the irradiation with electrons, to the production of isolated active points by the sigma rays associated with the alpha particles.