Long-range intramolecular electron transfer in azurins.

Area of Science:

• Biochemistry
• Biophysics
• Electron Transfer

Background:

• Azurins are blue single copper proteins found in various bacteria.
• These proteins play roles in electron transport chains.
• Understanding their redox properties is crucial for bioenergetics.

Purpose of the Study:

• To investigate the reduction mechanism of Cu(II) sites in azurins from Pseudomonas aeruginosa and Alcaligenes spp.
• To elucidate the role of the disulfide bridge in the electron transfer process.
• To analyze long-range intramolecular electron transfer using Marcus theory.

Main Methods:

• Pulse radiolysis to generate CO2- radicals for protein reduction.
• Spectroscopic analysis to detect radical intermediates and measure reaction rates.
• Temperature-dependent kinetic studies to determine activation parameters.

Main Results:

• Azurin reduction occurs in two distinct phases: fast bimolecular and slow unimolecular.
• Reduction of the disulfide bridge to a radical ion is coupled with Cu(II) reduction.
• Evidence suggests intramolecular electron transfer from the disulfide bridge to the Cu(II) site.
• Kinetic and thermodynamic parameters correlate with structural and redox properties.

Conclusions:

• Azurins facilitate long-range intramolecular electron transfer between their disulfide bridge and Cu(II) site.
• Marcus theory effectively explains the observed electron transfer rates and activation parameters.
• Variations in azurin structure and reactivity influence electron transfer efficiency.