Emission spectra from copper proteins containing type-3 centres.

Area of Science:

• Biochemistry
• Biophysics
• Spectroscopy

Background:

• Copper proteins with type-3 centers, such as ceruloplasmin, tyrosinase, and hemocyanin, are crucial metalloproteins.
• These proteins play vital roles in biological processes, and understanding their photophysical properties is essential.

Purpose of the Study:

• To investigate the luminescence properties of copper proteins with type-3 centers.
• To explore the origin of fluorescence in these systems and its potential link to specific functional groups.

Main Methods:

• Excitation of aqueous copper protein solutions within their absorption bands (325-345 nm).
• Analysis of luminescence spectra, emission peaks (415-445 nm), and decay times (≤10 ns).
• Comparative studies using carboxylic acids, amino acids, copper(II) carboxylates, acetic anhydride, and polypeptides.

Main Results:

• Copper proteins showed typical luminescence spectra with emission peaks at 415-445 nm and decay times under 10 ns.
• Strong analogous fluorescence was observed in concentrated carboxylic acid and amino acid solutions, also absorbing around 330 nm.
• Fluorescence was less intense in copper(II) carboxylate solutions and absent in solutions lacking free carboxyl groups.

Conclusions:

• A novel fluorescence phenomenon was observed in the studied copper proteins.
• The fluorescence is tentatively attributed to interactions involving carboxyl groups of amino acids near the active site.
• This finding provides insights into the photophysical behavior and structural features of type-3 copper proteins.