Purification and characterization of eosinophil cationic protein from normal human eosinophils

ECP (eosinophil cationic protein) was purified in high yield from the granules of human buffy coat eosinophils obtained from healthy individuals. The separation procedure included gel filtration on Sephadex G-75, ion-exchange chromatography on Bio Rex 70, and chelating chromatography on zinc-chelate Sepharose 6B. The normal ECP is a single-chain, highly cationic glycoprotein which separates on SDS-polyacrylamide gel electrophoresis into at least 3 molecular weight forms, with molecular weights of 18.5, 20 and 22 kDa. A heterogeneity in charge was also observed, with the 18.5 kDa form being the most cationic one. The various molecular species of ECP exhibited antigenic identity, identical amino acid compositions, and identical amino-terminal amino acid sequences. The molecular heterogeneity was shown to be caused by differences in glycosylation of the protein.