Complete amino acid sequence of a histidine-rich proteolytic fragment of human ceruloplasmin.

Abstract

The complete amino acid sequence was determined for a fragment of human ceruloplasmin [ferroxidase; Fe(II):oxygen oxidoreductase, EC 1.16.3.1]. The fragment (designated Cp F5) contained 159 amino acid residues and had a MW of 18,650. It lacked carbohydrate, was rich in histidine and contained 1 free cysteine that may be part of a copper-binding site. This fragment was present in most commercial preparations of ceruloplasmin, probably owing to proteolytic degradation, but could also be obtained by limited cleavage of single-chain ceruloplasmin with plasmin. Cp F5 probably was an intact domain attached to the COOH-terminal end of single-chain ceruloplasmin via a labile interdomain peptide bond. A model of the secondary structure predicted by empirical methods suggested that almost 1/3 of the amino acid residues were distributed in .alpha. helices, about 1/3 in .beta.-sheet structure, and the remainder in .beta. turns and unidentified structures. Computer analysis of the amino acid sequence did not demonstrate a statistically significant relationship between this ceruloplasmin fragment and any other protein, but there was some evidence for an internal duplication.