Immunochemical investigation on human ceruloplasmin. Partial explanation of the "heterogeneity"

Human ceruloplasmin from fresh serum has been purified by chromatography on hydroxyapatite and Con A-Sepharose. Quantitative immunoelectrophoretic analysis of fresh serum, stored serum and fractions from the different purification steps for human ceruloplasmin has been carried out. A combination of the latter, advanced technique with amino acid analysis, molecular weight determination by size chromatography, urea treatment, staining for oxidase activity and enzymatic proteolysis, has revealed that: 1) human cerulplasmin is a heterogeneous mixture of two glycoproteins (x) differing only in their carbohydrate content and 2) the protein part contains at least one very labile peptide bond which upon enzymatic hydrolysis gives rise to peptides with molecular weights of 93,000 (y) and 24,000 (z) dalton, respectively. The two glycoproteins are immunochemically identical. The y peptide is immunochemically partially identical, and the z peptide immunochemically non-identical, with the parent molecule. The y and z peptides are non-identical. On the basis of these observations a simplified two-dimensional model of human ceruloplasmin is proposed.