Lysozyme modification by the fenton reaction and gamma radiation.
A comparative study was performed on lysozyme modification after exposure to Fenton reagent (Fe(II)/H2 O2) or hydroxyl radicals produced by y radiation. The conditions were adjusted to obtain, with both systems, a 50% loss of activity of the modified ensemble. Gamma radiation modified almost all types of amino acid residues in the enzyme, with little specificity. The modification order was Tyr > Met = Cys > Lys > Ile + Leu > Gly > Pro = Phe > Thr + Ala > Trp = Ser > Arg > Asp + Glu, with 42 mol of modified residues per initial mole of native enzyme. In contrast, when the enzyme was exposed to the Fenton reaction, only some types of amino acids were modified. Furthermore, a smaller number of residues (13.5) were damaged per initial mole of enzyme. The order of the modified residues was Tyr > Cys > Trp > Met His > Ile + Leu > Val > Arg. These results demonstrate that the modifications elicited by these two free radical sources follow different mechanisms. An intramolecular free radical chain reaction is proposed to play a dominant role in the oxidative modification of the protein promoted by gamma radiation.
Edwards
Ana M
AM
Facultad de Química, Departamento de Química Física, Pontificia Universidad Católica de Chile, Santiago.
Ruiz
Marcelo
M
Silva
Eduardo
E
Lissi
Eduardo
E
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005720:Gamma Rays; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000494:pharmacology; D007501:Iron / Q000494:pharmacology*; D009113:Muramidase / Q000187:drug effects* / Q000528:radiation effects*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species
D000596:Amino Acids; C045076:Fenton's reagent; D017382:Reactive Oxygen Species; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D007501:Iron; C421864:hen egg lysozyme; D009113:Muramidase