Binding and uptake of copper from ceruloplasmin.

Specific binding of [67Cu]ceruloplasmin to plasma membrane containing preparations from rat tissues was shown in the presence of an excess of nonradioactive Cu(II) or ceruloplasmin. With Cu(II) there was positive cooperativity and an apparent KD of 10(-7) M. The effects of both "cold" ligands was partly additive. No "specific" binding was shown with Zn(II), unrelated proteins and after boiling the membranes. Total and specific binding of [67Cu]ceruloplasmin were 2-7 fold greater for heart and brain than for liver preparations, per g tissue or per mg protein, +/- correction for yield of 5'-nucleotidase. Cu(II) also inhibited uptake of [67Cu] from ceruloplasmin by CHO cells, but monensin did not, suggesting uptake of ceruloplasmin Cu occurs at the cell surface.