A study of the reduction and oxidation of human ceruloplasmin. Evidence that a diamagnetic chromophore in the enzyme participates in the oxidase mechanism.

Abstract

The stopped‐flow technique was utilized to measure the 610 and 340 nm absorbances of human ceruloplasmin during oxidation and reduction reactions. The results confirm earlier observations that the chromophores giving rise to these absorbances are different electron acceptors. Under steady state conditions both chromophores were partially reduced which indicates that they participate in the oxidase reaction. Oxidation rates for the 610 and 340 nm chromophores of completely reduced ceruloplasmin were too high to be compatible with the respective steady state absorbances. These results, together with a comparison of the oxidation rates for Type 1 copper of partially and completely reduced protein, showed that the oxidation rate for one chromophore is influenced by the oxidation states of the other and/or the nonchromophoric paramagnetic copper (Type 2). Therefore, the oxidase mechanism appears to involve concerted transfer of electrons from the 610 and 340 nm chromophores and possibly Type 2 copper.