Quantitate and monitor intracellular cathepsin K activity over time in vitro. The Magic Red reagent in this assay fluoresces red upon cleavage by active cathepsin enzymes. Analyze the fluorescent signal using fluorescence microscopy or a fluorescent plate reader.

Go to Full Product Details

Magic Red® Cathepsin K Assay Kit
SKU: 939

Size: 25 Tests
Sale price$199.00

Bulk Order Magic Red® Cathepsin K Assay Kit

Elevated cathepsin enzyme activity in serum or the extracellular matrix can signify a number of pathological conditions. ICT’s Magic Red assay kits are used by researchers seeking to quantitate and monitor cathepsin activity in cultured cells and tissues. This Magic Red assay kit detects cathepsin K activity. The Magic Red reagent MR-LR2 enters each cell in a non-fluorescent state. If cathepsin enzymes are active, the Magic Red substrate is cleaved and the cresyl violet fluorophone will become fluorescent upon excitation. As enzyme activity progresses and more Magic Red substrate is cleaved, the signal will intensify, allowing researchers to watch the color develop over time. Samples can be analyzed by fluorescence microscopy or fluorescent plate reader. Samples may also be analyzed with Acridine Orange or Hoechst stain to detect lysosomal organelle structure or nuclear morphology respectively.
Cathepsin K
592 nm / 628 nm
Fluorescence Plate Reader, Fluorescence Microscope
Cell culture
Domestic: Overnight Delivery; International: Priority Shipping
United States
  1. Prepare samples and controls
  2. Reconstitute Magic Red by adding 50 µL DMSO.
  3. Dilute Magic Red 1:10 by adding 450 µL diH2O.
  4. Add 20 µL Magic Red to each sample (~ 500 µL aliquot of cultured cells).
  5. Incubate while protected from light.
  6. Watch color start to develop within 15 minutes.
  7. If desired, label with additional stains, such as Hoechst, DAPI, Acridine orange, or an antibody.
  8. If desired, fix or embed cells.
  9. Analyze with a fluorescence microscope or fluorescence plate reader. Magic Red has an optimal excitation at 592 nm and emission at 628 nm.

If working with adherent cells, please see the manual for additional protocols.

Kit 939: 25 Tests
  • Magic Red Reagent (MR-LR2), 1 25-test vial, #6135
  • Hoechst 33342 Stain, 1 mL, #639
  • Acridine Orange Stain, 0.5 mL, #6130
  • Kit Manual
  • Kit 940: 100 Tests
  • Magic Red Reagent (MR-LR2), 1 100-test vial, #6136
  • Hoechst 33342 Stain, 1 mL, #639
  • Acridine Orange Stain, 0.5 mL, #6130
  • Kit Manual
  • Product Specific References

    PMID Publication
    36810735Ng, PY, et al. 2023. Sugar transporter Slc37a2 regulates bone metabolism in mice via a tubular lysosomal network in osteoclasts. Nature communications, 906.
    37625588Noda, K., et al. 2023. Characterization of Rab32- and Rab38-positive lysosome-related organelles in osteoclasts and macrophages. The Journal of biological chemistry, 105191.

    Question: Can we fix cells after magic red staining and then permeabilize and incubate with LAMP1 antibody to co-stain for lysosomes?

    Answer: We have not done any fixation procedures with this substrate but others have used a 4% paraformaldehyde treatment for 30 minutes with cold storage to extend their viewing time. Cleavage of the aspartic carboxyl frees up two primary-secondary amino groups that can react with the aldehyde functionality of the formaldehyde molecules. They don’t have the nice reactivity of a classic free amino group like you find on a lysine for instance but they are reactive and apparently fixable.

    Question: My second question was if I can permeabilize cells afterfixation followed by labelling cells with LAMP-1/2 antibody to visualize lysosomes, would that work?? I am afraid of using acridine orange which cannot be used in same cells and may overlap with magic red. This LAMP labeling may help me to ascertain lysosomal vs cytoplasmic location of cathepsin since my major interest is to look for lysosomal membrane permeabilization. If you any other product related to LMP or any other advice which can be used for magic red staining in context of LMP, please do let me know.

    Answer: We don’t foresee any issues with your proposed antibody labeling following Magic Red staining provided the fluorophore tag on the LAMP antibody is compatible with the fluorescence emission spectrum of the cleaved Magic Red substrate dye (cresyl violet). Acridine Orange is included in the kit to visualize lysosomal structures, however you are correct that using Magic Red substrate and Acridine Orange in the same cells should be avoided because of the overlap in emissions. We have not personally attempted to co-stain with other lysosomal markers beside Acridine Orange (AO) so unfortunately I can’t offer further advice. We intend to add an additional 2 or 3 lysosomal staining probes to our company product offering listings. But presently, we only included an example of AO staining to support the premise that our Magic Red substrates are capable of penetrating both the cell and lysosomal lipid bilayer membrane structures. Once inside lysosomal structures, our Magic Red cathepsin substrates can be converted into a fluorescent form of the substrate and detected by fluorescence microscopy techniques.

    Question: I am writing you because I have a question and to let you know that I was able to fix the MagicRed CTSK probe in tissue and extend the life a couple of days. My question is, do you know the molecular weight of the MagicRed Cathepsin K probe?

    Answer: The molecular weight of Magic Red Cathepsin K Substrate (MR(LR)2) is 1068.

    Related Products

    Recently viewed