A spectral study of human ceruloplasmin

The absorption, luminescence and CD spectra of human ceruloplasmin were studied. The absorption spectrum in the infrared, and the CD spectrum in the ultraviolet, both indicate the presence of β conformation in the native structure of the protein. From the magnitude of the measured ellipticity, it is estimated that 0.46 of the amino acid residues are in the β conformation, the remaining 0.54 being in an unordered form. A comparison of the fluorescence and phosphorescence properties of native and apoceruloplasmin shows that the presence of copper causes the quenching of tryptophanyl luminescence, probably through energy transfer to the copper chromophores. By the combined resolution of the absorption and CD spectra, it was concluded that the copper chromophores are involved in six electronic transitions in the region 300-900 nm. Our results provide evidence for an interaction between the copper chromophores responsible for the 330 nm absorption in ceruloplasmin.