ESR studies of γ-irradiated histone octamer and the histone H3

ESR spectrum of neat histone H3 γ-irradiated and observed at 77 K with low microwave power and modulation amplitude showed multiple resolved structure depicting nonequivalent interaction of the unpaired electron located at amido-carbonyl radical anion [–)NH–] of the peptide backbone with adjacent –NH– group and the β-proton of –CH group. The predominance of amido-carbonyl radical anion is in good accord with the expected partition of secondary electrons amongst the various electrophilic groups including peptide carbonyl and aromatic acid residues. Following a gradual rise of annealing temperature to room temperature, a double splitting spectrum from the well known -carbon amido radical was evolved.