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Cu(I) analysis of blue copper proteins.

P M Hanna¹, R Tamilarasan, D R McMillin

¹Department of Chemistry, Purdue University, West Lafayette, IN 47906.

The Biochemical Journal

|December 15, 1988

Summary

This study introduces a simple colorimetric test to measure Cu(I) in blue copper proteins. The method accurately determines copper valence states, crucial for understanding enzyme function and developing new derivatives.

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Area of Science:

Biochemistry
Analytical Chemistry
Bioinorganic Chemistry

Background:

Blue copper proteins play vital roles in biological redox processes.
Accurate determination of copper valence states is essential for understanding protein function.
Existing methods for Cu(I) determination can be complex or lack specificity.

Purpose of the Study:

To develop a simple and reliable colorimetric assay for quantifying Cu(I) in blue copper proteins.
To validate the assay using well-characterized proteins like plastocyanin, azurin, and stellacyanin.
To investigate the copper valence states in laccase and its derivatives.

Main Methods:

A colorimetric method utilizing 2,2'-biquinoline complexation in an acetic acid medium.
Analysis of spinach plastocyanin, Pseudomonas aeruginosa azurin, and Rhus vernicifera stellacyanin.
Quantification of Cu(I) in laccase and type-2-depleted laccase samples, with and without EDTA treatment.

Main Results:

The assay confirmed that the cysteine residue in type 1 sites does not induce Cu(II) reduction.
An endogenous reductant in laccase was identified, but its interference was eliminated by EDTA.
25% of type 3 copper ions in resting laccase were Cu(I), increasing to 80% in type-2-depleted laccase.

Conclusions:

The developed colorimetric method provides a straightforward approach for determining Cu(I) content in blue copper proteins.
The findings clarify the role of cysteine in copper reduction and quantify copper valence states in laccase.
This assay is valuable for characterizing metal centers in native and modified blue copper proteins, aiding in the development of new enzyme derivatives.

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