SensoLyte® Cathepsin Assays – B, D, E, G, K, L & S

Cathepsins (CTS's) are a family or proteases found in eukaryotic cells.1 Involved in many important physiologic processes, cathepsins can be classified as serine proteases (Cathepsins A & G), aspartic proteases (Cathepsins D & E) and cysteine proteases (Cathepsins B, C, F, H, K, L, O, S, W, V & Z).1

AnaSpec is pleased to offer a series of fluorimetric long wavelength, sensitive SensoLyte® 520 assay kits for enzyme activity determination of Cathepsins G, D, E, B, K, L and S. These kits employ a FRET (Fluorescence Resonance Energy Transfer) peptide substrate that emits in the green range of 520 nm, with excitation at 490 nm. The advantage of using longer wavelength emitting substrates means that autofluorescence from cellular components and test compounds is minimal; thus making the kits more sensitive. Furthermore, the use of HiLyte™ Fluor 488 (except for Cathepsin S, which uses 5-FAM) as the FRET donor (fluorophore) results in a more stable fluorescent signal, since HiLyte™ Fluor 488 is resistant to acidic pH.


Figure 1. A schematic representation of a FRET peptide as found in SensoLyte® 520 Cathepsin kits (except for Cathepsin S which uses 5-FAM instead of HiLyte™ Fluor 488) in which the fluorescence of HiLyte™ Fluor 488 is released after enzymatic cleavage.

Table 1. A listing of the SensoLyte® Cathepsin kits. Kits providing conventional FRET (Mca/Dnp) or fluorogenic substrates for cathepsins are also available.


Catalog #

SensoLyte® 520 Cathepsin B Assay Kit *Fluorimetric*


SensoLyte® 440 Cathepsin B Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin D Assay Kit *Fluorimetric*


SensoLyte® 390 Cathepsin D Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin E Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin G Assay Kit *Fluorimetric*


SensoLyte® Rh110 Cathepsin G Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin K Assay Kit *Fluorimetric*


SensoLyte® Rh110 Cathepsin K Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin L Assay Kit *Fluorimetric*


SensoLyte® Rh110 Cathepsin L Assay Kit *Fluorimetric*


SensoLyte® 520 Cathepsin S Assay Kit *Fluorimetric*


SensoLyte® 440 Cathepsin S Assay Kit *Fluorimetric*


Figure 2. Titration of Cathepsin D with peptide substrates with the same sequence, but different FRET pairs.
Substrates were incubated with different dilutions of Cathepsin D for 1 hour. HiLyte™ Fluor 488/QXL™ 520-based cathepsin substrate provided better sensitivity and signal/background ratio than the same peptide sequences coupled with the 5-FAM/QXL™ 520 or Mca/Dnp FRET pair.

Click "The Optimization of FRET Substrates for Detection of Cathepsins Activity" to view a poster presented at a previous scientific conference.

Please contact us ( to request for cross-reaction information of these kits or for technical inquiries on these and other SensoLyte® assay kits.


  1. Conus, S. Medical Intelligence doi:10.4414/smw.2010.13042.