Single-chain structure of human ceruloplasmin.

Abstract

In many reports human ceruloplasmin has been shown to contain several polypeptide chains. Their molecular weights have been estimated to 17000 and 59000. These findings formed the basis for proposed models of ceruloplasmin quarternary structure. Recently it was however observed, that the low molecular weight peptide chains found in commercial samples of human ceruloplasmin are absent if the protein is prepared directly from fresh serum, and evidence was presented that the earlier observed subunits were the result of limited proteolysis.The subunit structure of human ceruloplasmin has now been reconsidered using the new preparation. The reduced and cyanoethylated protein has been studied in solutions of 6 M guanidine hydrochloride. Its intrinsic viscosity and sedimentation coefficient, as well as data from gel filtration on calibrated columns of agarose gels are consistent with the presence of a single continuous polypeptide chain of about 1050 amino acid residues with a molecular weight around 120000. Together with the carbohydrate this accounts for the molecular weight of the native protein as determined by sedimentation equilibrium.