The purification of human caeruloplasmin

Abstract

A method for the purification of ceruloplasmin from the G 2 fraction of human plasma is described. Protein precipitation at various pH values and concentrations of NaCl in the presence of diethyl ether is followed by chromatography on diethylaminoethylcellulose. Partly purified ceruloplasmin is stable to freeze-drying only when rapid initial freezing is used. Highly purified ceruloplasmin is partly inactivated when freeze-dried under the same conditions. Purified material has a Cu/N ratio of 0.0197-0.0203 (w/w) and gives a single broad symmetrical peak on starch-gel electrophoresis. The values of the Cu/N ratio agree reasonably with a molecular weight of 151 000 and 8 atoms of Cu per molecule. On hydroxylapatite and diethylaminoethylcellulose chromatography, in addition to the main ceruloplasmin peak, a trace of a second peak with oxidase activity is eluted. The significance of this is discussed. Some enzymic properties of purified ceruloplasmin are briefly described.