Charge polymorphism in human lung cell pro-cathepsin B

Secreted pro-cathepsin B of HS-24 human lung-tumour cells, human alveolar macrophages and Wi-38 human lung-fibroblast cells was pre-purified by ion exchange chromatography and investigated by 2D gel electrophoresis. Four (Wi-38), six (HS-24) and ten (alveolar macrophages) polypeptides differing in charge, but with the same molecular mass of 45 kDa, were found. The isoelectrical points of these polypeptides ranged from 5.43 to 6.57. Deglycosylation reduced the mass (7 kDa) but did not change the charge pattern. This investigation established cell type-specific patterns of secreted pro-cathepsin B-forms, but only parts of these may be cell type-specific forms depending on differentiated expression of mRNA and post-translational modification.