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Unpaired electron migration between aromatic and sulfur peptide units
W A Prütz1, J Butler, E J Land
1Universität Freiburg, Institut für Biophysik und Strahlenbiologie, Federal Republic of Germany.
Free Radical Research Communications
|January 1, 1986
Summary
Cysteine thiyl radicals can oxidize tyrosine, with reduction potentials differing by 80 mV at pH 9.15. Methionyl radicals can generate indolyl radicals, requiring direct contact for intramolecular transitions.
Area of Science:
- Biochemistry
- Chemical Kinetics
- Free Radical Chemistry
Background:
- Understanding electron transfer in biological systems is crucial.
- Amino acid radicals play significant roles in biological processes.
- Free radical reactions are fundamental to many biochemical pathways.
Purpose of the Study:
- To investigate the one-electron oxidation capabilities of cysteine thiyl radicals.
- To determine the reduction potentials of cysteine and tyrosine radical couples.
- To explore electron transfer mechanisms involving methionine and tryptophan radicals.
Main Methods:
- Pulse radiolysis techniques were employed to generate and study radical species.
- Equilibrium constant measurements were used to determine redox potential differences.
- Spectroscopic analysis was utilized to identify radical intermediates and reaction products.
Main Results:
- Cysteine thiyl radicals were shown to oxidize tyrosine with an equilibrium constant of K5 = 20 +/- 4 at pH 9.15.
- The reduction potential difference between cysteine and tyrosine radical couples was determined to be 80 mV at pH 9.15.
- Methionyl radical cations reacted with tryptophan-glycine to form indolyl radicals, indicating specific reaction pathways.
Conclusions:
- Cysteine thiyl radicals are effective one-electron oxidants for tyrosine.
- Intramolecular electron transfer between tryptophan and tyrosine radicals requires direct contact.
- The study elucidates pathways for unpaired electron migration between peptide units.