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Functional Activity Frequently Asked Questions

Recombinant Protein Product Line

Q. What types of recombinant proteins does eBioscience offer?

The majority of the recombinant proteins eBioscience offers are cytokines and chemokines. However, we do offer an expanding list of various factors (growth, stimulating, etc.) as well.

Q. What formats do you offer?

eBioscience offers recombinant proteins, as well as carrier free recombinant proteins. The recombinant proteins are provided in a sterile buffer (formulation on individual Technical Data Sheets) with the addition of a carrier protein, which in most cases is 1% BSA. The carrier free recombinant proteins are provided in a sterile buffer (formulation on individual Technical Data Sheets) with no additional proteins or preservatives.

Q. What is the shelf life of your recombinant proteins?

The majority of eBioscience recombinant proteins have a guaranteed shelf life of one year unless indicated on our Technical Data Sheets. This guarantee is provided if that they are kept under optimal storage conditions as stated on the Data Sheet (at -80°C). If you are not completely satisfied with the performance of your product, please contact technical support at for assistance.

Q. What are the concentrations of the recombinant proteins offered?

In most cases, the recombinant proteins are offered at a concentration of 0.1mg/mL, while the carrier free recombinant proteins are offered at 0.5mg/mL. However, we do recommend you refer to the product vial for lot specific information.

Q. How should I store my recombinant protein(s)? Can I dilute them upon receipt?

You will want to store the recombinant proteins at or below -80°C. The proteins can be diluted, and specific information regarding this is available on the Technical Data Sheets. However, key considerations are as follows:

  1. Always quick spin the vials prior to opening
  2. Dilute primary stock to a minimum of 10ug/mL
  3. Perform dilutions in a buffered saline (formulation on technical data sheet) which contains 1.0% BSA or 10% FBS as a protein carrier/stabilizer
  4. Make aliquots to minimize the number of freeze/thaw cycles. Avoid freezers with thermal cycling, such as frost free freezers.

Q. What is the specific activity of eBioscience recombinant proteins?

The specific activity (Units/mg) for each recombinant protein is available on the Technical Data Sheet under Bioactivity. The information can also be found in our Bioassays- Recombinant Cytokines and Recombinant Growth Factors Quick Guide on our Best Protocols® page.

Q. What is meant by a 'unit' of protein activity?

A "unit” is defined as the concentration of protein required to induce half maximal activity (e.g. in ng/mL). This is also referred to as the ED50, or 50% effective dose. This method of expressing potency should only be used for proteins whose dose response curves are sigmoidal in shape (e.g. not chemotaxis assays).

Q. What is the relationship between the specific activity (Units/mg) and ED50 of a protein?

The formula for converting the activity as an ED50 in ng/ml to a specific activity in Units/mg is:
Specific activity (Units/mg) = 10e6/ ED50 (ng/mL)

Q. Does each lot of recombinant protein have the same specific activity?

No, each lot can vary slightly with regards to its specific activity. The information on the Technical Data Sheet for each product is provided as a guide. For lot specific information, please contact eBioscience Tech Support.

Q. What is the difference between laboratory (observed) units and international units?

Laboratory units are the actual values obtained from running an assay with a particular protein in an assay in your lab; i.e., the activity (ED50) you observe on your target cells. ‘International’ units are consensus values of potency derived from a collaborative NIBSC effort to standardize reported use of proteins. These values are derived from bioassay testing of the same protein by many target cell types/substrains. It is very likely that the ‘laboratory’ units you observe and the NIBSC values will not correlate 1:1; e.g., it might take 0.1 - 20 U/mL to see 1 U/mL in your experiment. These are bioassay standards describing potency in bioassay only. The mass values assigned to these are not hard values and use of these for immunoassay standardization is of limited value unless assays calibrated by the NIBSC standard use the same capture and detection antibody clones.