Abstract
| - The one-electron reduction of hen egg white lysozyme has beenreinvestigated by γ-radiolysis usingCO2•-free radicals as reductants. We show that the reaction is specifictoward one out of the four disulfide bridges,i.e. the 6−127 one. This bond is in interaction with the chargedend of arginine 5. The reduction leads tothiol functions and to a lesser extent to fragmentation of thepolypeptide chain, which can only come fromelectron migration from disulfide. To get a better insight intothe mechanism induced by electron transfer tothe protein, the 6−127 disulfide bridge and the charged end ofarginine 5 in lysozyme were modelized byR2S2 (R = H, CH3) andC(NH2)3+, andab-initio calculations were performed.All separate molecular andradical entities resulting from the electron addition were optimizedwith two basis sets (6-31G* and 6-31+G*)and at the MP2 correlation level. The formation of complexes wasstudied and four zwitterionic and twoneutral radical complexes involved in charge transfer reaction werecharacterized at the MP2 level. Theinfluence of the environment was taken into account by using theOnsager reaction field method (SCRF) forthe isolated species as well as the complexes.
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