Spectroscopic and photoreduction studies of copper chromophores in ceruloplasmin.

Photoreduction of native ceruloplasmin, using the 454.5-nm line of an Ar+ laser, enables the identification of type-Ia, type-Ib and type-II copper. The circular dichroic spectra of N--3-bound type-II copper and SCN-- -bound type-II copper are obtained by the same procedure after anionic treatment of ceruloplasmin. From circular dichroic and resonance Raman evidence it appears that some of type-Ia and type-Ib copper ligands differ. Type-Ib copper ligands seem to the same as type-I copper in plastocyanin and azurin. Even though type-Ib copper is coordinated to one sulfur of cysteine and one sulfur of methionine (or disulfide of cystine), the methionine sulfur is not a ligand for type-Ia copper.