Presence of reduced type 1 copper in ceruloplasmin as revealed by reaction with hydrogen peroxide.

The reaction of hydrogen peroxide with ox or sheep ceruloplasmin leads to approximately 10% increase of the optical absorption band at 610 nm and of the Type 1 EPR signal. No inactivation or denaturation of the protein is apparent up to 15 H2O2 molar excess. Oxygen is able to restore about 50% of the Type 1 copper absorption in ascorbate-reduced ceruloplasmin, while the other half is recovered after addition of H2O2. It appears that H2O2 undergoes a specific redox reaction with ceruloplasmin, which reveals a fraction of the total copper to be present in the native protein as reduced copper. This fraction is apparently Type 1 copper, while Type 2 is not affected by H2O2.