Divalent cation binding to ceruloplasmin

Binding of calcium to human and sheep ceruloplasmin was investigated by metal substitution with manganese and competitive displacement of bound manganese by calcium monitored by electron paramagnetic resonance spectroscopy, The K-d for calcium was found to be 1.4 mM. Magnesium also bound to ceruloplasmin, with K-d = 0.3 and 0.7 mM for the human and sheep protein, respectively, The thermal stability of ceruloplasmin, as studied by differential scanning calorimetry, was affected by calcium but not by magnesium, A considerable increase of the T-m value, from 73.8 to 83.1 degrees C, was observed for sheep ceruloplasmin in the presence of calcium, The T-m value of the human protein was only slightly altered by calcium (from 85.1 to 87 degrees C), The interaction of ceruloplasmin with the chromatographic material used for its isolation, Sepharose 4B derivatized with chloroethylamine, was weakened by calcium, This allowed us to set up a novel purification scheme that made it possible to efficiently isolate ceruloplasmin and prothrombin from plasma with the same single-step chromatography.