Analysis of cathepsin D from breast tissues by capillary electrophoresis

A rapid and simple method for analyzing cathepsin D in breast tissue based on capillary zone electrophoresis (CZE) is described. After incubating the tissue extracts with hemoglobin as a substrate, a specific peptide is cleaved and separated by CZE in less than 5 min. This peptide is not produced by the action of pepsin or trypsin. It is inhibited by the addition of pepstatin, a specific inhibitor for cathepsin D. Human hemoglobin acted as a better substrate than bovine hemoglobin. The test compared well to a radioimmunoassay. We have shown that peptides can be stacked by the use of acetonitrile. The method demonstrates the advantages of CZE for assay of proteolytic enzymes in general.