| Assay Method Information | |
| | In Vitro Enzymatic Cathepsin D (CatD) FRET Assay |
| Description: | Recombinant CatD was expressed in CHO cells. The assay buffer for CatD was 0.05 M citrate pH 3.5, 10% DMSO final, 5 mM CHAPS. The CatD enzyme (9 nM) was pre-incubated for one hour with inhibitors, typically in about 1 uL of DMSO according to a serial dilution, is added thereto. The assays was effectively started by the addition of different FRET substrates (20 nM for CatD) and the combination was incubated for one hour. The FRET assay was terminated with by addition of tris buffer, which raises the pH to neutrality, and the fluorescence was determined. The FRET substrate was a peptide with commercially available fluorophore and quencher, on opposite sides of the CatD cleavage site. The CatD substrate peptide sequence was based on sequence #1 of Table 1 from Gulnik et al., FEBS Lett. 413(2):379-384 (1997). Proteolytic cleavage of the FRET substrate released quenching of fluorescence (CatD excitation 500 nm and emission 580 nm).Alternatively, a CatD assay may also be run according to the procedure described in Yasuda et al., J. Biochem. 125(6):1137-1143 (1999). In addition, the CatD and Cathepsin E assays are described in International Patent Application Publication No. WO2011069934. |
| Affinity data for this assay | |
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