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

ESR spectrum of neat histone H3 gamma-irradiated and observed at 77 K with low microwave power and modulation amplitude showed multiple resolved struc ture depicting nonequivalent interaction of the unpaired electron located a t amido-carbonyl radical anion [-CHRC(O-)NH-] of the peptide backbone with adjacent -NH- group and the beta-proton of -CH group. The predominance of a mido-carbonyl radical anion is in good accord with the expected partition o f secondary electrons amongst the Various electrophilic groups including pe ptide carbonyl and aromatic acid residues. Following a gradual rise of anne aling temperature to room temperature, a double splitting spectrum from the well known alpha-carbon amido radical was evolved. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.