Spin transfer from protein to DNA in X-irradiated ’dry‚ and hydrated chromatin: an electron spin resonance investigation of spectral components between 77K and room temperature

Purpose : To investigate the potential total and relative free-radical transfer from histones to DNA in X-irradiated chromatin, by analysing the relative contributions of individual radicals from protein and from DNA. Materials and methods : Chromatin was isolated from calf thymus, freeze-dried and either used as such or after equilibration at 76% relative humidity. A mixture of histones was purchased. Xirradiation was performed at 77K (liquid nitrogen). Data acquisition was on a Bruker ESP 380 ESR-spectrometer (X-band, 9.5GHz) and at high magnetic fields (285 GHz, Y-band, GHMFL Grenoble). Data analysis involved computer treatment of spectra. Results : Three components were isolated from an annealing series of histones and assigned to specific radicals (X-band). Chromatin revealed the existence of radicals from both DNA, as well as from the histone compartment. The presence of the oxidized guanine base, as well as the reduced cytosine and thymine bases from DNA at 77 K was confirmed by high-field ESR. Rel...