Radiation damage to histone H2A by the primary aqueous radicals

Histone H2A has been examined for radiation-induced changes in structure and in amino acid composition. The effects of the individual radical intermediates--the hydroxyl radical, solvated electron, and superoxide radical--have been determined by irradiating in dilute aqueous solution under controlled environmental conditions. Amino acid analysis of irradiated histone H2A shows a selective attack on a few residues; only the aromatic residues, phenylalanine and tyrosine, and the heterocyclic residue, histidine, are significantly decreased. A significant increase in aspartic acid is also observed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that the hydroxyl radical is the effective radical for promoting changes in protein structure.