Does the peroxidase-like activity of sodium dodecyl sulphate-modified cytochrome c increase after peroxynitrite or radiation treatment?
The peroxidase-like activity of cytochrome c is considerably increased by unfolding of the protein. The enhancement of the activity is due to the higher reaction rate of unfolded cytochrome c with hydrogen peroxide, which is the rate-determining step in the peroxidase cycle of cytochrome c (Gebicka, L., 2001, Res Chem Intermed 27, 717-23). In this study we checked whether combined action of two unfolding factors, SDS and peroxynitrite or radiation (hydroxyl radicals), increases the peroxidase-like activity of cytochrome c more than any single treatment alone. Peroxynitrite reacts with SDS-modified cytochrome c in the same way as with native cytochrome c, via intermediate radical products, *OH/*NO2, arising from peroxynitrite homolysis. We found that SDS-modified cytochrome c is much more sensitive to oxidative damage than the native protein. Partial unfolding of cytochrome c by SDS causes the peroxide substrate to have a better access to the heme center. On the other hand, the amino acids located in the vicinity of the active site and/or heme group become accessible for oxidizing radicals. The overall effect observed is that the peroxidase-like activity of SDS-modified cytochrome c decreases with an increase of the concentration of the oxidizing species (peroxynitrite or radiolytically generated hydroxyl radicals). The damage of SDS-modified cytochrome c caused by irradiation is much more significant than that observed after peroxynitrite treatment.
Gebicka
Lidia
L
Institute of Applied Radiation Chemistry, Technical University of Łódź, Łódź, Poland.
Didik
Joanna
J
D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects* / Q000528:radiation effects*; D005720:Gamma Rays; D017665:Hydroxyl Radical / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000494:pharmacology*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*
D030421:Peroxynitrous Acid; D017665:Hydroxyl Radical; D012967:Sodium Dodecyl Sulfate; D045304:Cytochromes c