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Intramolecular long-range electron transfer in the hemerythrin monomer: a pulse radiolysis study
1Department of Chemistry, Nuclear Research Centre-Negev, Beer-Sheva, Israel.
Biochemical and Biophysical Research Communications
|January 30, 1990
Summary
Methemerythrin
Area of Science:
- Biochemistry
- Protein Chemistry
- Electron Transfer Studies
Background:
- Methemerythrin is an iron-containing protein involved in oxygen transport.
- Understanding electron transfer mechanisms in proteins is crucial for bioenergetics.
- The role of specific amino acid residues in protein redox activity requires investigation.
Purpose of the Study:
- To investigate the intramolecular electron transfer pathway in Phascolosoma gouldii methemerythrin.
- To characterize the kinetics and thermodynamics of electron transfer from a modified sulfhydryl group to the protein's iron center.
Main Methods:
- Chemical modification of the methemerythrin's single sulfhydryl group (Cys-50) using 5,5'dithiobis(2-nitrobenzoic acid).
- Pulse radiolysis to generate formate radicals for reduction of the mixed disulfide.
- Differential pulsed polarography to determine the redox potential difference between the two centers.
Main Results:
- A mixed disulfide was formed at Cys-50, which could be reduced by formate radicals.
- The disulfide radical anion facilitated intramolecular electron transfer to the protein's two-iron center.
- The rate constant for this electron transfer was determined to be approximately 15 s-1 at room temperature and pH 7.
- An equilibrium driving force of 0.78 V was measured between the redox centers.
Conclusions:
- The Cys-50 residue plays a role in mediating electron transfer in methemerythrin.
- Intramolecular electron transfer occurs over a distance of 13 Å.
- The study provides insights into the kinetics and energetics of electron transfer in metalloproteins.
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