Lysozyme modification by the Fenton reaction and gamma radiation

Loading...
Thumbnail Image
Date
2002
Journal Title
Journal ISSN
Volume Title
Publisher
TAYLOR & FRANCIS LTD
Abstract
A comparative study was performed on lysozyme modification after exposure to Fenton reagent (Fe(E)/H2O2) or hydroxyl radicals produced by gamma 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.
Description
Keywords
lysozyme, gamma radiation, Fenton reaction, hydroxyl radical, BIOLOGICALLY RELEVANT, OXYGEN RADICALS, PROTEIN DAMAGE, PEPTIDE-BOND, AMINO-ACIDS, OXIDATION, INACTIVATION, DEGRADATION, PHOTOOXIDATION, TRYPTOPHAN
Citation