Decrease in Accessible Thiols as an Index of Oxidative Damage to Membrane Proteins

The effect of several oxidative agents (hydrogen peroxide, tert-butyl hydroperoxide, menadione, AAPH, peroxynitrite and ionizing radiation) on the ratio of weakly to strongly immobilized residues of erythrocyte membrane-bound maleimide-tempo spin label (hw/hs ratio) was studied in order to test the hypothesis that a decrease in the hw/hs ratio may be a general index of oxidative damage to membrane proteins. Most of the agents studied decreased though H2O2 almost did not affect and ionizing radiation increased the hw/hs ratio. In parallel, the ratio of DTNB accessible/DTNB inaccessible membrane protein —SH groups was determined from membrane —SH group measurements with the Ellman reagent in the absence and in the presence of sodium dodecyl sulfate. This ratio decreased in all cases studied and seems to be a more universal and easy to measure parameter to describe the oxidative damage to membrane proteins.