Molecular forms of ceruloplasmin in hepatolenticular degeneration and their interaction with human erythrocyte ceruloplasmin receptor.

Immunochemical methods were used to show that the sera of homozygous and heterozygous carriers of the Wilsonian gene contain, together with normal ceruloplasmin (CP), a CP-like protein that differs from CP in its enzymatic, immunological, and physicochemical properties. The CP-like protein was isolated from the sera of patients with hepatolenticular degeneration (HLD) by means of affinity chromatography, and monospecific antibodies to this protein were obtained. The presence of an 80 kDa immunoreactive polypeptide specific to the CP-like protein was demonstrated by immunoblotting with antibodies to normal CP and monospecific antibodies to the CP-like protein. Analysis of the ratios of the molecular forms of CP in homozygous and heterozygous carriers of the Wilsonian gene indicated that this ratio reflects the dosage of the mutant gene. The kinetic parameters of the interaction of these proteins with the CP-specific receptor on the erythrocyte membranes from healthy individuals and from patients with Wilson's disease (HLD) were determined. The CP receptor on erythrocyte membranes in HLD patients is not altered and its interaction with normal CP has the same kinetic parameters as the binding of normal CP to the erythrocyte receptors from healthy individuals. The CP-like protein also retains the ability to bind to the CP-specific receptor but the ligand-receptor complex is less stable than in the case of normal CP. The possible mechanism of the molecular heterogeneity of CP in the Wilsonian mutation is discussed.