Recombinant C. difficile Toxin B/TcdB Protein, CF

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Recombinant C. difficile Toxin B/TcdB Protein, CF Summary

Product Specifications

>95%, by SDS-PAGE under reducing conditions and visualized by Colloidal Coomassie® Blue stain at 5 μg per lane
Endotoxin Level
<1.0 EU per 1 μg of the protein by the LAL method.
Measured by its ability to hydrolyze UDP-Glucose. The specific activity is >45 pmol/min/μg, as measured under the described conditions.
E. coli-derived c. difficile Toxin B/TcdB protein
Met1-Leu543, with a C-terminal 6-His tag
Accession #
N-terminal Sequence
Predicted Molecular Mass
64 kDa
60-65 kDa, reducing conditions

Product Datasheets

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Carrier Free

What does CF mean?

CF stands for Carrier Free (CF). We typically add Bovine Serum Albumin (BSA) as a carrier protein to our recombinant proteins. Adding a carrier protein enhances protein stability, increases shelf-life, and allows the recombinant protein to be stored at a more dilute concentration. The carrier free version does not contain BSA.

What formulation is right for me?

In general, we advise purchasing the recombinant protein with BSA for use in cell or tissue culture, or as an ELISA standard. In contrast, the carrier free protein is recommended for applications, in which the presence of BSA could interfere.


Formulation Supplied as a 0.2 μm filtered solution in Tris and NaCl.
Shipping The product is shipped with polar packs. Upon receipt, store it immediately at the temperature recommended below.
Stability & Storage: Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
  • 6 months from date of receipt, -20 to -70 °C as supplied.
  • 3 months, -20 to -70 °C under sterile conditions after opening.

Assay Procedure

  • Assay Buffer: 25 mM Tris, 150 mM NaCl, 10 mM MnCl2, 5 mM CaCl2, 150 mM K2SO4, pH 7.5
  • Recombinant C. difficile Toxin 1B/TcdB (rCdTcdB) (Catalog # 6246-GT)
  • Coupling Enzyme: Recombinant Human CD39L3/ENTPD3 (rhCD39L3) (Catalog # 4400-EN)
  • Substrate: UDP-Glucose (Calbiochem, Catalog # 670120), 10 mM stock in 25% ethanol
  • Malachite Green Phosphate Detection Kit (Catalog # DY996)
  • 96-well Clear Plate (Costar, Catalog # 92592)
  • Plate Reader (Model: SpectraMax Plus by Molecular Devices) or equivalent
  1. Dilute UDP-Glucose to 1.6 mM in Assay Buffer.
  2. Dilute rhCD39L3 to 16 µg/mL in Assay Buffer.
  3. Prepare reaction mixture by combining 200 μL UDP-Glucose and 200 μL rhCD39L3 (sufficient for ~15 wells).
  4. Dilute rCdTcdB to 10 µg/mL in Assay Buffer.
  5. Dilute 1 M Phosphate Standard by adding 10 µL of the 1 M Phosphate Standard to 990 µL of deionized water for a 10 mM stock. Continue by adding 10 µL of the 10 mM Phosphate stock to 990 µL of Assay Buffer for a 100 µM stock (this is the first dilution of the standard curve).
  6. Prepare six additional one-half serial dilutions of the 100 µM Phosphate stock in Assay Buffer. The standard curve has a range of 0.078 to 5.0 nmol per well.
  7. Load 50 µL of each dilution of the standard curve into a plate. Include a curve blank containing 50 μL of Assay Buffer.
  8. Load 25 µL of the 10 µg/mL rCdTcdB into the plate. Include a substrate blank containing 25 µL of Assay Buffer.
  9. Add 25 µL of reaction mixture to the wells, excluding the standard curve.
  10. Cover the plate with parafilm or a plate sealer and incubate at room temperature for 40 minutes.
  11. Add 30 µL of the Malachite Green Reagent A to all wells. Mix and incubate for 10 minutes at room temperature.
  12. Add 100 µL of deionized water to all wells.
  13. Add 30 µL of the Malachite Green Reagent B to all wells. Mix and incubate for 20 minutes at room temperature.
  14. Read plate at 620 nm (absorbance) in endpoint mode.
  15. Calculate specific activity:

     Specific Activity (pmol/min/µg) =

Phosphate released* (nmol) x (1000 pmol/nmol)
Incubation time (min) x amount of enzyme (µg)

     *Derived from the phosphate standard curve using linear or 4-parameter fitting and adjusted for Substrate Blank.

Per Well:
  • rCdTcdB: 0.25 µg
  • rhCD39L3: 0.2 µg
  • Substrate: 400 µM
Reconstitution Calculator

Reconstitution Calculator

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Background: Toxin B/TcdB

Clostridium difficile is the leading cause of hospital-acquired diarrhea, known as C. difficile-associated disease. The estimated number of cases of C. difficile-associated disease exceeds 250,000 per year (1), with health care costs approaching US $1 billion annually (2). The major virulence factors produced by C. difficile are two toxins, TcdA and TcdB. Both toxins can monoglucosylate and inactivate Rho family small GTPases within target cells, leading to disruption of vital signaling pathways in the cell, subsequently causing diarrhea, inflammation, and damage of colonic mucosa (3, 4, 5). Both toxins have a similar tripartite structure comprised of an N‑terminal glucosyltransferase domain, a C-terminal receptor binding domain, and a small hydrophobic span possibly involved in toxin translocation (6). Our recombinant TcdB consists of the enzymatic domain. Both TcdA and TcdB also have potassium-dependent UDP-Glc hydrolase activity, which is essentially glucosyltransferase activity with water as the acceptor molecule (7). Under same conditions, UDP-glucose hydrolysis by TcdB occurs at a rate about 5-fold greater than that of TcdA.

  1. Wilkins, T.D. and Lyerly, D.M. (2003) J. Clin. Microbiol 41:53.
  2. Kyne, L. et al. (2002) Clin. Infect. Dis. 34:346.
  3. Voth, D.E. and Ballard, J.D. (2005) Clin. Microbiol. Rev. 18:247.
  4. Chaves-Olarte, E. et al. (1996) J. Biol. Chem. 271:6925.
  5. Just I, et al. (1995) J. Biol. Chem. 270:13932.
  6. Hammond, G.A. and Johnson, J.L. (1995) Microb. Pathog. 19:203.
  7. Ciesla, W.P. Jr. and Bobak, D.A. (1998) J. Biol. Chem. 273:16021.
Entrez Gene IDs
4914074 (C. difficile)
Alternate Names
TcdB; toxB

Product Specific Notices

Coomassie is a registered trademark of Imperial Chemical Industries Ltd.

Citations for Recombinant C. difficile Toxin B/TcdB Protein, CF

R&D Systems personnel manually curate a database that contains references using R&D Systems products. The data collected includes not only links to publications in PubMed, but also provides information about sample types, species, and experimental conditions.

4 Citations: Showing 1 - 4
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  1. NLRP3 licenses NLRP11 for inflammasome activation in human macrophages
    Authors: A Gangopadhy, S Devi, S Tenguria, J Carriere, H Nguyen, E Jäger, H Khatri, LH Chu, RA Ratsimandr, A Dorfleutne, C Stehlik
    Oncogene, 2022;23(6):892-903.
    Species: Human
    Sample Types: Whole Cells
    Applications: Bioassay
  2. Investigation of the adsorption capacity of the enterosorbent Enterosgel for a range of bacterial toxins, bile acids and pharmaceutical drugs
    Authors: CA Howell, SV Mikhalovsk, EN Markaryan, AV Khovanov
    Sci Rep, 2019;9(1):5629.
    Species: Bacteria Toxins
    Sample Types: Gel Constructs
    Applications: Bioassay
  3. Treatment ofClostridium difficileinfection with a small molecule inhibitor of toxin UDP-glucose hydrolysis activity
    Authors: IL Stroke, JJ Letourneau, TE Miller, Y Xu, I Pechik, DR Savoly, L Ma, LJ Sturzenbec, J Sabalski, PD Stein, ML Webb, DW Hilbert
    Antimicrob. Agents Chemother., 2018;0(0):.
    Species: Bacteria - Clostridium difficile
    Sample Types: Chemical Compound
    Applications: Bioassay
  4. Pyrin inflammasome activation and RhoA signaling in the autoinflammatory diseases FMF and HIDS
    Authors: Yong Hwan Park
    Nat Immunol, 2016;0(0):.
    Species: Mouse
    Sample Types: Whole Cells
    Applications: Bioassay


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